Knives Chau from Scott Pilgrim, to the extent of not only stalking him, but attacking Ramona (Scott's Current Girlfriend) twice and building a shrine to Scott. She got better, though.
Wannabe from Wildguard: Casting Call, a secretly powerless heroine desperate as Hell to hit the superhero big time and more than willing to hurt anyone who gets in her way. She also wears her costume all the time, even after the competition is over and she isn't actually superheroing anymore.
Mercy Mayrock from Howard Chaykin's The Shadow miniseries. A former beauty queen turned game show host whose violent on-air meltdown ruined her career... until she met quadriplegic billionaire Preston Mayrock, the real Lamont Cranston, and married him. She's also completely obsessed with the Shadow (eventually attempting to rape him at gunpoint and telling him to keep his costume on) and is sexually aroused by nuclear weaponry and explosions.
In DC's Identity Crisis, Jean Loring, Ray Palmer's (the Atom) longtime ex-wife, has a nervous breakdown and becomes one of these for her ex-husband. While maintaining a facade of being contently divorced, she planned to put superheroes' families in danger so that all heroes (including Ray) would run to their loved ones, ending in the deaths of three people. She was only slightly unhinged until she accidentally killed Sue Dibny, at which point she completely lost it.
Batman villain Harley Quinn may seem cute, but anybody who gets between her and "Mistah Jay" will regret it... if they live long enough.
An episode of Batman: The Animated Series had Harley getting closer than anyone else to killing Batman because Joker was spending all his time obsessing over him instead of her.
And an issue of the BTAS comic book switched the roles. Joker is rendered sane and gentle by intense electroshock therapy, and actually starts treating Harley with affection. She can't stand it and tries to get him to return to his old personality, but he has no interest in violence and mayhem anymore. But when Batman shows up and Joker refuses to fight him, Harley announces that she loves Batman. Wherepon Joker says that he'll "just have to rip Batman's lungs out" to keep her, and immediately returns to his old self.
This trait is carried over in the DC Reboot even though Harley and Joker are in different series. Harley is first seen hunting down and murdering the lawyers who put Joker away over the years in a desperate bid to get his attention after he left her.
The Venom Symbiote is a total Yandere for Spider-Man. Its thought process can be summed up as "That bastard! How dare he kick me out! Didn't he realize how awesome I was?! Well screw him! I hate him, I hate him, I want him to die! He deserves to suffer for hurting me! But then... I won't have him! I know, I'll kill off everything he loves and then force him to take me back! Then it will just be us together forever..."
It's even been lampshaded, once in Marvel Age Spider-Man and in The Spectacular Spiderman, both times Peter pretends to apologize and asks if it wants him to be its host again, which it does, and both times Peter mentions it's acting like a jealous ex-girlfriend.
Also take a look at the What If? take on The Other storyline. Peter doesn't come back to life and the symbiote immediately abandons its current host to merge with Peter's body, becoming a new monstrosity called "Poison". It wants Peter so badly it doesn't even mind that Peter is dead.
Spider-Man's former wife Mary Jane was actually plagued by two male versions of this Trope, which were, oddly enough, connected. The first, and more obvious one, was her wealthy and Axe Crazy landlord Jonathan Caesar. His first attempt to kidnap her failed, leading to his arrest and imprisonment, but even while behind bars, he was able to use his money and influence to make her life miserable, blacklisting her among the modeling profession until she managed to gain a role in the Secret Hospital soap opera.
The second one was much more subtle. After Caesar was paroled, a few folks who assaulted or abused Mary Jane (including a deluded fan of the soap opera and her angry director) were either murdered or assaulted. Mary Jane suspected it was Caesar's doing, especially when Peter himself was almost a victim, but Peter tended to doubt it, claiming that the attacks didn't fit his MO. Peter turned out to be right. The true culprit was the second Yandere (known only by his last name, Goldman) who had claimed to be a policeman, but was really only a clerk working for the NYPD. When Caesar made a second attempt to kidnap Mary Jane, Goldman murdered him in cold blood, and when Mary Jane rejected him, tried to shoot her too. But she tricked him into to getting close by offering to reveal the future plot of the soap (saying they'd have to change it if she were dead) and was able to knock him out with her purse. (Kind of makes you wonder what she kept in it... Bricks?)
Iron Man's armour became Yandere towards him at one point after it achieved sentience. Jocasta had accidentally infected the armour with Ultron's AI, which was altered when the suit was struck by lightning. While it initially proved far superior to his other suits, it made the Venom symbiote look positively tame in comparison, although it eventually sacrificed itself to save Tony's life after accidentally beating him to death.
Played with in Yoko Tsuno's story The Pray And The Shadow. The Yandere is actually an adult man in his late 40's, Mac Nab, who as a youngster was spurned by his crush Lady Mary and showed up at her wedding to curse her and her new husband, Brian, and predict that they'd never be happy. Brian died within the year, Mary almost fell into madness and some years later died in an accident, and everyone blamed Mac Nab, who was barely able to clear his name yet was ostracized by the community, living alone in a small house and keeping a mannequin that looks exactly like Mary and wears her wedding dress. The truth? William, Brian's brother and Mary's second husband, set up poor Mary for death and made it look like an accident, then brewed an Evil Plan to kill Mary and Brian's daughter Cecilia so he could get her huge inheritance. Mac Nab was still a yandere for Mary, but once he learned the truth he remained focused enough to join Yoko's plans to rescue Cecilia (as well as her Body Double Margaret) and use the mannequin as a Spanner in the Works.
Fortunately, once the Sapphires organized into a Corps, their matrons, the alien Zamarons, externalized their power, swapping out the parasitic crystal for a ring and power battery like the Green Lanterns, allowing the Star Sapphires to maintain more of their normal personality. The Violet Light of Love still alters their behavior more than all of the other lights except Red do, however.
Veronica Pace in Strangers in Paradise. After the Big Bad's "suicide", her former chauffeur Veronica takes over the remains of her organisation, gives herself an Evil Makeover and begins to show signs of Ax Craziness. Before her defeat, she reveals that she did it all because she was obsessed with Katchoo.
Power Boy became a Yandere for Supergirlthe moment he laid eyes on her on Apokolips. He was so obsessed with her that he couldn't even eat or sleep after she left. He traveled to Earth and played the role of a superhero hoping he could get her to fall for him. His act was so good that Supergirl actually dated him for a few issues. Then his jealousy over Supergirl's friendship with Captain Boomerang Jr. reached a peak and drove him to assault and imprison her. Supergirl, understandably upset, promptly broke free of her restraints and ended their relationship — with a Groin Attack. In his latest appearance he's shown regularly having sex with women who look like Supergirl - and at his insistence, wear the costume the whole time.
This was all intended as a parody/deconstruction of the way your average Distaff Counterpart is often introduced or portrayed, as it happens.
In Secret Six Black Alice goes Yandere for Ragdoll. Calling him beautiful, inviting herself over to his place, declaring that Ragdoll is her boyfriend, turning into a demon and attacking his lesbian teammate Scandal because she thought Scandal was making a move on Ragdoll...as Ragdoll himself puts it: "I'm not the one being creepy here."
Superman has had not one, but TWO Yanderes after him:
The first and most prominent was Maxima, Queen of the planet Almerac. Maxima learned about Superman after viewing a transmission of outer-space gladiator games that Superman was forced to take part in, and set out to make the Man of Steel her mate. Since Superman rejected her advances, Max periodically attempted to wreak revenge, including an alliance with his nemesis Brainiac. She had also been known to set her sights on other heroes, sometimes in less violent ways (her attempted romance with Amazing Man during the period she was a reformed heroine), sometimes much more so (kidnapping Aquaman).
The second was an Earth woman named Dana Dearden. She always fascinated by the legends of ancient gods. Since the Man of Steel is more-or-less a modern-day god, she transferred her interest to him, filling her room with various news clippings and other memorabilia of him. After stealing some ancient coins at the local museum, she gained superpowers and donned a hero costume of her own, insisting that she was Kal-El's Super-Woman. But not only did Superman deny her the love she sought, she was quickly given the somewhat irritating name "Obsession". In her fury, she destroyed an oil tanker, and disappeared for awhile. And when Obsession resurfaced during Superman's split into Red and Blue versions, she ran up against Maxima, who wasn't interested in Dana's suggestion that there was now one Supes for each of them. In the end, though, Obsession's love for Superman proved 100% true, when she sacrificed herself to save him from a magical attack.
In Anya's Ghost, it's part of the twist ending that Emily lied about her past, having in fact killed her would-be boyfriend and his actual girlfriend out of jealousy.
Kriss de Valnor from Thorgal proves to be one in Shaigan story arc. She has a crush on Thorgal and just cannot take that he loves Aaricia and won't return her feelings and tried to murder her at least once. After Thorgal suffers complete amnesia thanks to the gods, she convinces him he is Shaigan the Merciless, ruthless pirate and her lover. That is understable, if evil. However convincing him to attack vikings from his home village, knowing very well that it will result in Aaricia's and her children being exiled, then kidnaping Aaricia and her daughter and, by holding the latter hostage, forcing the former to serve her and amnesiac Thorgal, who doesn't even recognize his own wife, as a slave and be forced to watch them making love every night, all just so Kriss can rub in her face that she had stolen her man - that's full yandere. It's a little wonder that French collected edition of the Shaigan arc is titled In the Claws of Kriss.
You... you're cheating on me with that Graphic Novel whore, aren't you?!Back to yandere or I'll tear your pages apart!