The hero has a Secret Identity, and so does the villain. On the days that they're not battling, they live or work uncomfortably close to one another - or at least it would be uncomfortable if they only knew who that guy across the room really was. But each one simply doesn't recognize the other one when the costumes are off (as if the voice wouldn't give it away in seconds). Often, they're even best friends or even dating in their uncostumed lives while fighting tooth and nail when in a cowl. Sometimes one of them is aware of it but chooses not to do anything whether due to manipulation, confidence, or not wanting to touch off a simmering powder keg.
They don't always live together; heroes and villains may work for the same company or go to the same school.
The Reveal tends to be... messy.
Compare Enforced Cold War, where the two sides know that each is the enemy, but are forced to co-exist anyway; Go-Karting with Bowser and Friendly Enemy, where the two sides know that each is the enemy and are friends in spite of it; and Keeping the Enemy Close, where one side holds the other within close proximity so they can't catch them off-guard, not to mention when one within their own ranks is a potential traitor. Villain Over for Dinner has both parties be aware of each other's identities but remain civil for the sake of their loved ones. Cain and Abel and Dating Catwoman can be subsets of this. See also Mutual Masquerade.
Examples:
- Akuma no Riddle is about an all girl class at a boarding school. All but one are assassins. Their target? The non-assassin. She's more aware than she lets on.
- Done more or less literally in Cat's Eye: the title characters are three sisters and thieves, even with good reasons (for starters, everything they steal was supposed to be their inheritance), and early on Toshio, one of the cops assigned to arrest them, moves in with them. He had been dating the middle sister Hitomi for a long time, so when his house burned down he asked them to let him stay for a while, Hitomi accepted to keep her romantic rival from doing it, and he ended up living there for good.
- In Catgirl Nuku Nuku Flash, an Alternate Continuity of All-Purpose Cultural Cat Girl Nuku Nuku, one of the villainesses of an organization that wanted to control the world was the mother of the young boy ward of Nuku Nuku. At home, she was a very loving, very caring mom who juggled her time between work and her family. At work, she was a cackling scenery chewer sending out the Monster of the Week.
- Code Geass:
- Lelouch Lamperouge leads a rebellion in Japan against the occupying Britannians, while his childhood friend Suzaku fights for them in a powerful mecha. Both are unaware of the other's secret life — Lelouch even wants to betroth Suzaku to his little sister at one point.
- Code Geass also has Kallen, Lelouch's best mecha pilot, unaware of either of their identities for some time. Then in R2 Lelouch has a sensei and a little brother by way of memory alteration both working for the Britannians. However Lelouch knew Kallen's secret from day one and did not actually befriend her until after he found out that she was a terrorist
- Then in R2, two Knights of the round joins Ashford Academy. In this show, half of the important characters of the world war joined Ashford Student Council at some point.
- In Code Geass: Nightmare of Nunnally, Nunnally's best friend, Alice, is one of the Irregulars as a Number who has received Geass abilities from CC's cells, and her mission is to capture or kill Nunnally as pilot of the Mark Nemo (but Alice doesn't know it's Nunnally). Nunnally is upset to learn that Alice is a Britannian soldier after being captured, but Alice then manages to rescue her, and the two reconcile.
- Crescent Moon is about protagansit Mahiru Shiraishi, who is helping a band of supernatural creatures called the Lunar Race. One of her classmates turns out to be a member of an order dedicated to hunting down and destroying the Lunar Race.
- D.N.Angel has protaganist Daisuke Niwa, who has a Superpowered Alter Ego as Phantom Thief Dark. He finds himself in conflict with classmate Satoshi, a teenage prodigy police commander who is tasked with the job of capturing Phantom Thief Dark, and whose family has been enemies of the Niwa family for generations. Despite this rivaly, Daisuke considers Satoshi his friend, however he also has to deal with Krad, who is Satoshi's Superpowered Evil Side.
- In the manga and anime Death Note, Light Yagami does this twice. The first is part of the basic set-up of the show: his father is one of the police inspectors investigating the killings Light is perpetuating. The second comes later, when Light and L, the master detective, go to the same university. L reveals who he is to Light, and L suspects Light of being "Kira," but their mutual uncertainty skews the trope in interesting ways. He even ends up being handcuffed together with L.
- Played with in Digimon Adventure 02: the heroes don't figure out that Ken is the Digimon Emperor right away, but Ken knows exactly who they are. And instead of going to school together, it's more that they know him from being a child star, and at one point, Ken and Davis' soccer teams square off in a match. Davis' team is doing decently well until Ken shows up and owns them.
- As of recent events in Durarara!!, the leaders of the Dollars, the Yellow Scarves and the Saika army are teetering on the edge of war. Just who are the three leaders? Mikado, Masaomi and Anri.
- Another Living with the Villain scenario occurs when Vorona joins Shizuo as one of Tom's bodyguards in order to pinpoint Shizuo's weaknesses and destroy him. She expected that he wouldn't recognize her — what she didn't expect was that Shizuo was so quiet-mannered and unassuming outside of his Hair-Trigger Temper and Unstoppable Rage that she'd barely be able to recognize him.
- One of the central tropes in Dokkoida?! is that the heroes' and villains' Secret Identities all live in the same apartment and don't recognize one another.
- Excel♡Saga. The apartments surrounding ACROSS agents Excel and Hyatt house members of the city government task force investigating ACROSS activities. Neither side knows they are living next door to their enemies until they move out.
- In Fullmetal Alchemist, it's quite some time before the heroes realize that one of the Homunculi they're desperately trying to defeat is actually Fuhrer King Bradley, the leader of the nation and head of the military. On top of that, another one is Bradley's young, seemingly-innocent son.
- In Jubei-chan 2 Freesia wormed her way into being adopted into Jiyu's family and was literally living in their house.
- In the first series, The Secret of the Lovely Eyepatch, many of Jiyu's opponents are her teachers. They don't last long in their positions.
- Kaitou Tenshi Twin Angel has the eponymous three magical girls in the same class. Their Mysterious Protector is also in the same class. He knows who they are, but they don't know who he is. Their Evil Counterparts and Black Carrier are their classmates and teacher, and neither side is aware of who the other is. Even though their costumes should give it away.
- To quote Nanoha Takamachi, "Wouldn't it be funny if the master of the Book of Darkness was someone my age?" Yeah, and it'd be even funnier if you had a mutual friend and visited each other. Nanoha gets a message from Suzuka introducing her to Hayate immediately after saying that.
- In the first A's sound stage, Nanoha and Fate almost meet Hayate and the Wolkenritter at a bath (Arisa meets Vita at one point but doesn't know who she is), and Suzuka considers introducing the two groups, but decides to wait until later. Shamal gets quite a shock in Episode 8 after learning that Nanoha and Fate are friends with Suzuka, who's friends with Hayate, and is thus forced to take precautions to make sure that they don't find out about Hayate being master of the book of Darkness.
- Mobile Suit Gundam 00 has Billy Katagiri from The Union crushing on a lady named Sumeragi Lee Noriega...who works for Celestial Being. Also, Gundam Meister Setsuna F. Seiei's neighbor is an Ordinary High-School Student named Saji Crossroads, who gets caught in the war in a VERY dramatic fashion.
- Mobile Suit Gundam 0080: War in the Pocket. Zaku Pilot Bernard "Bernie" Wiseman is on an infiltration mission to destroy the prototype Gundam Alex hidden in the local colony and befriends one of the local kids, Al, and his older cousin Christina "Chris" Mackenzie. What Bernie doesn't know is that Chris is the test pilot for the Alex and, tragically, ends up having to face her and the prototype when his mission is botched and the entire colony was going to be nuked in response. To make it worse, After Bernie is killed, Al finds out about Chris's status as the Alex's pilot but chooses not to tell Chris, which makes it worse as both end up telling him to say goodbye to the other (Bernie doing so on a tape he made in case he was killed).
- In Nabari no Ou, protaganist Miharu Rokujou finds himself attacked by a subsititue teacher, who turns out to be a member of a ninja clan that wants to abduct him.
- In Negima! Magister Negi Magi, child teacher Negi Springfield finds himself at various times fighting against several of his students. This causes him great consternation, because he feels that it is his duty as a teacher to help rather than harm his students.
- In the anime Nurse Witch Komugi, the secret identity of the main villain is the heroine's possessed best friend. This is revealed in the opening sequence.
- A tragic case appears in Outlaw Star. When child assassin Hanmyo attacks Jim Hawkings' ship, both ships are damaged and land at a nearby planet for repairs. Both Jim and Hanmyo meet, and having never seen each other, don't realize that the other is an enemy. They have a fun time together and decide to meet again later for a date. The repairs complete, both launch... and Hanmyo is killed, in a hurry to finish her assignment and see Jim again. Jim gets back in time for his date, but Hanmyo never shows up. He never learns of her death or his part in it.
- A pivotal point in Phantom Thief Jeanne: Junior police girl Miyako does not know that Maron is Kaitou Jeanne, and neither realize that Chiaki is Kaitou Sinbad, despite all living on the same apartment floor.
- Subverted in the manga, where Miyako reveals that she did figure out that Marron was Jeanne, but knew she must be stealing paintings for a certain reason. Whether she knew about Chiaki being Sindbad is never mentioned, though.
- In the anime Prétear the main character's new stepmother's maid turns out to be the Princess of Destruction.
- In the Pretty Sammy series, a Tenchi Muyo! spinoff, Pretty Sammy and her enemy Pixy Misa are actually Sasami and her best friend Misao. This is more excusable than most examples, because Pixy Misa has an entirely different personality than the shy Misao, and Misao herself is unaware of her other self until nearly the end of the series.
- The villains Ali and En from the "Makaiju" arc of Sailor Moon were disguised as schoolmates of most of the Senshi. The same applied with Chibi-usa's friend Hotaru (possessed by Mistress 9, The Dragon to that series Big Bad) in the third season, and the Witches Five, who worked at Michiru and Haruka's Elaborate University High. In Ami's introduction episode, Luna suspects this of her, but learns she's actually another Sailor Senshi instead.
- Star Driver: Some of the Glittering Crux members go to the heroes' school. The school nurse is found out, though Takuto doesn't seem to have picked out any of his classmates that he fought against. The masks do this somehow. When Sugata wears one, it's not recognized until it is too late.
- Of course, considering this is a giant robot show, and Takuto's Tauburn doesn't have optical zoom or a radio, he's not really close enough to see anything. Especially when they're inside a robot, trying to kick his ass.
- Takuto does eventually figure out who he fights against, however, particularly if the villain for the day reveals his Signature Move which Takuto also experienced outside of Zero Time. Despite this, particularly with members of Filament and Adult Bank, they remain amiable towards each other in ordinary life.
- In Tantei Opera Milky Holmes, the four heroines are attending school, where the four villains are one of their teachers, the Student Council President, a classmate and a janitor. Despite the villains not acting any differently than normal (except for maybe Arsene), they haven't caught on.
- In the Time Bokan series Otasukeman both the heroes and the villains work in the same police Space Station as Time Police. Both the antagonist trio (which later becomes a quartet) and the good guys have secret identities; the former group as Ojamaman, who try to alter history following the whims of the Big Bad, and the latter group as the titular Otasukeman, who always manage to put everything back in place.
- In Witch Craft Works, the group of Tower Witches under Medusa (including Medusa) eventually start living at the house of the Takamiyas. One amusing omake has Ayaka in charge of feeding them. She throws them a bar of chocolate to be shared among all six of them while she feeds Honoka blowfish nabe.
- Bakura of Yu-Gi-Oh! goes to Yugi's school and is considered a friend by most of Yugi's company. However, his alter ego is revealed to be the Big Bad at the final season.
- This happens very often in the sequel series, Yu-Gi-Oh! GX. Saiou, Amon Garam and Yusuke Fujiwara all enroll at Duel Academy at some point. And then there's Professor Cobra...
- YuruYuri's Show Within a Show, "Majokko Mirakurun", has Magical Girl Kurumi/Mirakurun and her rival majokko Rivalun, who is secretly Raika, Kurumi's friend and classmate.
- Arch Enemies: A superhero and his Arch-Enemy supervillain share an apartment as their secret identities. Not only do they completely fail to recognize each other, but each hates their roommate much more than their Arch-Enemy.
- Spider-Man (Peter Parker) and the Green Goblin have this kind of relationship in the early Spider-Man comics, as the Goblin is actually Norman Osborn, the father of Peter's best friend, Harry. The trope then gets subverted after Norman dies, and Harry takes up the Goblin mantle; Peter and Harry soon discovered each other's identities, but Peter couldn't do anything about it without losing his chance to cure Harry's madness. For his part, Harry kept Peter's identity secret just to have a bit of leverage to mind-screw him with.
- Mary Jane ended up demanding they all sit down and have a nice family dinner, and in the end, she was actually the one who got through to Harry. You can guess what happened next.
- In fact, there's a common fan joke Peter is plagued with this kind of bad luck, since many of his famous opponents tend to be people he already knows.
- At one point, Peter moved in with a cop, Vin Gonzales. Which would not be a bad solution... except that Spidey is an unregistered superhero, suspected of being a serial killer, hunted by Venom, Kraven's daughter, Green Goblin... And Parker is unemployed and can't afford the rent. Vin turned out to be helping frame Spider-Man for being a serial killer, and later joined a cult worshiping the Green Goblin. Yeah. Parker luck.
- In one issue of the Marvel Adventures continuity, Aunt May decides to rent out a free room in the Parker household. Who moves in? Doctor Octopus! What happens next? HE HITS ON AUNT MAY.
- This is in reference to a story in the 70's in which Dr. Octopus nearly married Aunt May.
- Even earlier in the mid-60s he had boarded with the Parkers, even after kidnapping Aunt May and Betty Brant during the Sinister Six's first appearance (though May didn't know it was a kidnapping).
- Nineties Marvel hero Thunderstrike had an enemy called Bloodaxe, whom he was certain was either his ex-wife (and mother of his child) or the ex's new boyfriend. This made for stressful family get-togethers, and at least one occasion where Thunderstrike alienated his ex, the boyfriend and his own son when he acted rashly. Bloodaxe turned out to be his new girlfriend Jackie, which is arguably worse.
- In a more literal example, one issue had Thunderstrike surprised to recognize his new roommate as his foe Stellaris, the Celestial Slayer, who had sworn revenge on him. Luckily, she'd changed her mind on that. Not bad for a series that only lasted 2 years.
- Robin (1993): Darla Aquista tries to force Tim to move in with her and become her boyfriend without ever realizing that he's also her sworn enemy Robin, whom she is trying to kill.
- Supergirl: Cosmic Adventures in the 8th Grade: Linda Lee, alias Supergirl, and Lena Thorul (real family name:Luthor) share a room in Stanhope Elementary's boarding house. Linda is aware of Lena's real identity, but she considers her a friend regardless. However, Lena hates all super-heroess -thanks to her brother's influence-, and she will blow her top -and the whole school- if she finds out her roomate's secret identity.
- Parodied in the comic strip Gorilla Gorilla, where Gorilla and Lizard are roommates that grow giant, repeat their names twice, and fight each other, having no idea no matter how painfully obvious their "secret" identities get.
- In MGLN Crisis, Raquel Benna, an elderly fruit seller whom Fate knows well, is a key figure in her investigation into her origins, having worked with Precia and Jail Scaglietti to help make "Clyde Harle", a clone of Clyde Harlaown so that Precia could have Alicia. Lindy suspects that she moved close to Fate in order to tell her the truth before she passed away.
- In Ace Of Spades, Harry befriends Bruce Wayne, not realizing he was Batman while Bruce didn't realize that Harry was the Joker's new sidekick called the Ace.
Acey: It's kind of funny though; friends in one identity, enemies in the other.
- In Harry Riddle when she began the affair Lily Evans Potter had no idea that that charming man Tom that she took as her lover was actually Voldemort. Also Harry and Draco's friendship with Hermione and Neville—the professors express doubts that Neville would be so chummy with Harry if he knew that Harry's "Auntie Bellatrix" tortured his parents into insanity.
- In the AU Heart of an Assassin after meeting, Light and L become quite taken with each other while both are blissfully unaware of the other's true occupations.
- Persona EG has two examples:
- The first major enemy that ZIT fights, Eris, turns out to be their friend Fluttershy. She continues to qualify as this after her identity is revealed, despite not openly attacking them anymore, until her official Heel–Face Turn on her birthday.
- Sunset Shimmer moves into the dorm with everyone in June, after spending most of the year trying to kill Flash and his friends. She claims that she has given up and has no interest in fighting them anymore since they have practically won already and have stopped every attempt she's made against them and their friendship, claiming she just wants to know how they did it. Everyone is still cautious and wants little to do with her in case she is lying.
- In A Fantastic Upheaval of Previously Held Notions, with a target painted on his back by the Janus Order, Strickler is unable to stay at his home. Because he is still magically bonded with Barbara, keeping his distance is a poor option and he has to stay with the Lake family with no choice in the matter.
- In the Three Houses fanfic You'll Get No Answers from the Blue Sea Star, it slowly becomes obvious that someone living in the monastery is a traitor. In fact there are two - Tomas, the head librarian, and Edelgard, one of the students. Both are revealed in rather dramatic fashion.
- Hidden in Silence: The Nazis force Fusia and Helen to board two German nurses for a nearby military hospital after nearly putting the hospital itself in her house. Since 13 Jewish refugees are hiding in the sisters' attic, this causes some tension. It doesn't help that the nurses' soldier boyfriends (at least one of whom is anti-semitic) also end up living there.
- Inverted in the Made For TV movie Re-Animated, where the lead, the villain, and the lead's Secret Keepers are the only ones who do realize the villain and the lead are literally living together—no matter how obvious the villain's evilness and bumbling murderous intentions become, the rest of the cast either fails to realize it or treats him like a harmless Cloudcuckoolander.
- This is the basis of the movie Mr. & Mrs. Smith (2005), wherein both characters put up a front of normal life for each other while they go about their real jobs as spies/assassins working for rival firms—until they're both given assignments that lead to their paths crossing.
- Prizzi's Honor is also about two professional hit-persons who are married to each other. Eventually, they discover that each has been hired to kill the other. They follow through, but only one succeeds.
- In the Animorphs series:
- Jake, the leader of the titular resistance force, knowingly spent years living with the Yeerk controlling his older brother Tom.
- Marco had the same situation with his mother, the host body for Visser One, except that he didn't find out about the Yeerks until after she had already faked her own death.
- The principal of the school turns out to be infested by the Yeerks. In order to keep up the masquerade, the heroes are forced to keep up the image of a good student while at school.
- In Bigtime, Karma Girl features a narrator who uses this fact as a way to track down and discover the secret identities of superheroes and villains.
- The Pendragon Adventure has Andy Mitchell, Mark and Courtney's delinquent classmate, whom they've known since kindergarten on Second Earth. He is really Saint Dane in disguise. There's also Telleo on the territory of Ibara, who is secretly Nevva Winter.
- In Interview with the Vampire, Louis sees his cohabitation with Lestat to be this after their relationship sours. Whether Lestat is a true villain with entitlement issues is uncertain thanks to Louis being an Unreliable Narrator and Lestat's character not yet being finalized.
- At one point in Les Misérables, Javert takes an apartment in the same lodging house as Valjean and Cosette are hiding in. Javert suspects his neighbor is Valjean, and Valjean recognizes Javert in time to flee, but briefly, this ensues.
- My Teacher Is an Alien. Hell, the title tells you all you need to know. Susan, Peter and Duncan are forced to face the enemy every single day! In the sequels, the titular aliens are revealed to have less-villainous motives.
- In Pyrates, George discovers, to his horror, that one of his favorite neighbors is the villain. Getting kidnapped by him in the second book makes him and his friends properly paranoid.
- Dimmesdale lived with Chillingworth in The Scarlet Letter.
- The Scholomance: The Last Graduate reveals that two mals have been living in Chloe's room for years, disguised as cushions. They've spent that time eating anyone else who's ever been alone in the room, while leaving the owner alive to avoid suspicion and draw in more victims (students coming early for study group sessions, etc.) The whole scene is pure Paranoia Fuel.
- Alias has Sydney and Alison Dorren living togther after Dorren kills Francie. Dorren has undergone a procedure to look exactly like Francie. Syd not only takes quite a while to figure it out, she even reveals she is a spy to "Francie" when she thinks her friends might be in danger.
- Breaking Bad has Hank and Walt as jovial companions, with Hank even feeding Walt details about the Heisenberg case. When Hank eventually finds out the Walt was Heisenberg all along to say he's angry is an understatement.
- This trope can also apply to Gus Fring's relationship with the DEA. He donates mass amounts of money to the DEA and is on first name bass with several of the agents, all while running the mass drug empire the DEA is trying to shut down
- Season One of Broadchurch follows two detectives who are investigating the murder of a boy in a small town. The killer turns out to be the husband of one of the detectives.
- Happens in Chousei Kantai Sazer X when Sazer-X captures Blaird and, lacking a convenient place to hold him, decides to keep him in the Ando household. It culminates in Blaird basically becoming an honorary member of the Ando family, after he tastes Haruko's cooking and starts to warm up.
- Dexter often lampshades this, commenting on how all of his co-workers are committed to catching murderers, yet no one (except Doakes) can figure out that he is one.
- In Dollhouse Tahmoh Penikett's character, who's set on destroying the Dollhouse, starts a relationship with the nice girl across the hall after she brings him dinner. Later, it's revealed that she's been a Doll the whole time, complete with a trigger phrase that turns her into an ass-kicking ninja.
- In the third season of The Flash (2014), Iris and Barry move in together. Neither of them knows at first that Savitar is a possible future version of Barry who's drawing upon his past self's memories.
- Kamen Rider Decade literally has this, as Eijiro Hikari, grandfather of the female lead Natsumi and owner of the photo studio that is the hub of the heroes, is revealed to be Dr. Shinigami. Not that he's aware of it himself at first, since he seems like he was under mind control when he transformed. Later, he does come to regret his actions as an executive of Dai-Shocker, and in the finale, is not too keen on going back into the Shinigami persona.
- Revenge greatly plays into this, with Emily Thorne (aka Amanda Clarke, daughter of the man framed for terrorism by the Graysons) dating, moving in with and becoming engaged to Daniel Grayson, the son of her arch nemesis Victoria. In addition to regularly attending family events hosted by the Graysons as Daniel's girlfriend/fiance, Emily's beach house is overlooked by Victoria's manor balcony allowing the latter to spy on her.
- In Season 3 Emily and Daniel marry, resulting in Emily briefly moving into Grayson manor. Due to her ulterior motives being partially revealed on her wedding night, the Graysons come to the mistaken belief that Emily is a gold-digging grifter and Emily in turn blackmails them with the identity of her shooter. Unsurprisingly, their living situation becomes extremely tense.
- Persona 3 has two notable examples:
- First, Shuji Ikutsuki turns out to be a Nietzsche Wannabe. To make things even worse, he has been manipulating SEES into doing his dirty work for him the entire time.
- And then there's Ryoji Mochizuki, who is even unaware himself that he is actually the avatar of Nyx, the Anthropomorphic Personification of Death destined to bring about The End of the World as We Know It.
- In Persona 4 the two major villains of the game Adachi and Izanami live and work within the town as a cop and gas station worker respectively for most of the game as friendly NPCs. In fact, near the end when the player must guess out who the killer is, your biggest hint is that it would be someone who would be completely welcome to the Dojima household. And in one of the earliest versions of the game the killer was your uncle, meaning you were literally living with him, but playtesters apparently found this so disturbing that this was changed during production.
- In Ar Tonelico 2: Melody of Metafalica, when you enter into Jacqli's Comsosphere, you are forced to take part in a play where Croix becomes a man named Kuroaki, Luca stays as Luca, and Cloche becomes Reish with Jacqli becoming Miwa after she starts the story. In the story, Miwa is a shy quiet girl that Kuroaki takes interest in, and after the third cosmosphere dive, it is revealed to Kuroaki that Miwa, the girl that he's in love with and that is falling for him is the Big Bad. Miwa even admits that she's fallen for Kuroaki but doesn't know how to stop hating people. At the end of the 5th cosmosphere dive, Kuroaki and Miwa enter an epic final battle while Luca and Reish are out cold. Kuroaki attempts to make Miwa come with him and be a better person. Before this can become completely resolved however, Jacqli pulls the plug on the story right there, waking everyone back up to reality without a proper ending to what happened to Kuroaki or Miwa.
- Not to mention Infel, who was posing as Cloche's Mind Guardian.
- In Banjo and Kazooie's reveal trailer for Super Smash Bros. Ultimate, Donkey Kong and Diddy Kong let King K. Rool sleep in their house.
- Tsukihime loves this trope; all of the Far Side route villains either live with Shiki or invade his home often enough that they may as well.
- This happens in Viewtiful Joe 2. Turns out that Jet Black, your dad, was the Black Emperor the whole time and used you in order to get the power he needs to rule the world.
- Downy Reed in Duel Savior Destiny is a spy for the forces of Ruin. When pressed about the apparent betrayal, the response is that it's no such thing. He was never on your side to begin with.
- In The Legend of Heroes: Trails of Cold Steel, your main protagonist, Rean Schwarzer, ends up living in a dorm room directly across from late-joining classmate Crow Armbrust, whose slacker-student mask hides the game's main villain, the terrorist leader "C."
- In Fire Emblem: Three Houses, no less than five villains are present undercover at Garreg Mach Monastery during your stint as a professor: Solon, disguised as the monastery librarian Tomas, Kronya, disguised as a previously kidnapped student named Monica, the Death Knight, whose true identity is the fencing instructor Jeritza, the Flame Emperor, whose true identity is the leader of the Black Eagles house, Edelgard, and Hubert, who does not have a dual identity but acts as the Flame Emperor's Secret-Keeper.
- In Bob and George, the titular characters lived together back in their own universe (as in, not the Mega Man universe) as they were brothers. George was a superhero, Bob a supervillain. Apparently, they both got powers from their mom.
- Man Man rents out the basement of his Man-Mansion to his nemesis Dr. Vivisectus, making it convenient for battles between them.
- In The Magnificent Milkmaid, the title character fights her own friends turned enemies, Chastity/Prixen and Martina/Sweater Puppy, a plot that also features in Chocolate Milkmaid.
- This Channelate comic plays with the trope.
- In Adventure Time, after Finn tricked Ice King and Flame Princess into fighting and the latter melted the Ice Kingdom, Ice King stayed with Finn and Jake until the kingdom was restored.
- In American Dragon: Jake Long, not only does Jake go to school with Rose (who is a Huntsgirl who hunts dragons like Jake), he has a crush on her. That is, of course, until they figure out they're sworn enemies at the end of the first season.
- In Batman Beyond, a few of the villains Terry McGinnis (Batman) faced were students or faculty at his high school. In this case, there isn't the arc-based component: the villain is revealed, and Terry is horrified to see the face of his classmate.
- The first season Big Bad was Bruce Wayne's business partner at Wayne-Powers Enterprises (not that Bruce liked him or anything).
- On DC Super Hero Girls, The female heroes and female villains all attend school together and frequent the same malt shop. Harleen "Harley Quinn" Quinzel and Barbara "Batgirl" Gordon are even best friends who are both unaware of the other's alter ego, in which they are sworn enemies.
- In Codename: Kids Next Door, one of the organization's Arch Enemies is Corrupt Corporate Executive Mr. Boss; Numbuhs Two, Three, and Four have a parent who works for his company, and oddest of all, Numbuh 86 (on of the KND's highest-ranking members) is his daughter. It hasn't caused any issues between them at all.
- Numbuh 5's sister, Cree, is a ranking evil teen. Both girls are stuck living in the same house and the only reason their parents haven't figured out that the two hate each other is because they are extremely oblivious.
- The series' Big Bad Father is eventually revealed to be Numbuh 1's uncle.
- In the Danny Phantom series, the title character has a crush on Valerie Gray, a demoralized girl from the popular crowd who has recently taken up ghost hunting. Danny, being a half ghost superhero, ignores his friends' warnings and tries to pursue a relationship with Valerie. She would like to be with Danny - if only that pesky ghost boy weren't around!
- Invader Zim: Zim and Dib attend the same school and class.
- Though in this case, they both KNOW they are arch-enemies, but no one else pays enough attention, or has the intelligence to believe either of them.
- Iron Man: Armored Adventures: Throughout most of the first season, Tony (Iron Man) and Gene (The Mandarin) attend school together and work together to find the Makluan rings they're both interested in, both in ignorance of the other's secret identity. This is at least justified by the fact both of them use suits that change their voices and completely hide their faces when going under their alias (Gene even becomes taller as the Mandarin), so no wonder they couldn't recognize each other.
- Kid vs. Kat, in which the main hero's sister's pet cat is an alien bent on conquering the Earth(Or sending cat treats to his home planet.)
- Subverted in Penn Zero: Part-Time Hero. Part-time heroes Penn, Sashi, and Boone are students at a high school where part-time villains Rippen and Larry work as art teacher and principal, respectively. All of them are aware of the situation, with their base of operations even being literally next-door to each other.
- Miraculous Ladybug: Adrien's father, Gabriel Agreste, is secretly the show's Big Bad Hawk Moth/Shadow Moth. One of his employees, Nathalie Sancouer, sometimes transforms into his Dragon Mayura. Adrien is completely unaware that he lives in his worst enemy's house.
- And the Hooded Claw, Penelope Pitstop's nemesis, was her guardian Sylvester Sneekley in real life. Yet another indication of the Southern belle's stupidity- he made no attempt to disguise his extremely distinctive voice and that nose of his was always visible.
- Penelope was more näive than stupid when it came to distinguishing the Claw from Sneekly. Sure, Sneekly's voice and nose should be a giveaway, but the rest of him and his demeanor kept Penelope from realizing his identity.
- The Sonic Boom episode “Can An Evil Genius Crash On Your Couch For A Few Days?”, has a literal example. Tails let’s Dr. Eggman temporarily stay at his house, and Sonic and Tails have to put up with him being a horrible roommate.
- Static Shock had this happen a few times as well - several of Static's enemies were classmates of his who had the residual effects from "the Big Bang" kick in at inopportune moments.
- In the Wolf and Sheepdog cartoons, Ralph Wolf and Sam Sheepdog treat each other as coworkers, literally punching a clock and exchanging "Mornin' Sam," "Mornin' Ralph" before the mayhem ensues. In a later cartoon they even share a house together.