A character starts out normal (as they can be anyway) with a crush on someone else and becomes more of a Stalker with a Crush / Yandere as the series goes on. They mainly become this way because of romantic reasons. Love Makes You Crazy after all. See also Sanity Slippage.
Examples:Anime and Manga
- Koharu of \'\'Koharu No Hibi\'\' gets more and more Yandere as the series progresses. She starts out doing things like confessing her love to Akira and making him food, continues by gluing her hands together with his, stalking him, saving his discarded bottles, and later covering her room with pictures of him and getting crazy looks on her face as she threatens/harasses her love rival.
- In \'\'Stepping on Roses\'\' Nozumu starts as a regular admirer of Sumi, but as the series goes on, his behavior becomes more erratic from kidnapping Sumi and trying to commit murder-suicide to taking over his best friend\'s company and demanding that Sumi marry him.
- Kotonoha and Sekai of \'\'School Days\'\' both start out as seemingly normal girls but as a result of Makoto cheating on them with other girls they end up loosing it. Sekai stabs Makoto to death and Kotonoha cuts off Makoto\'s head and kills Sekai as well as cutting open her stomach to check if she was pregnant.
- \'\'Mahou Sensei Negima!\'\' has the secondary villain Tsukuyomi. She starts as a mere Punch-Clock Villain with shades of Psychopathic Manchild and a crush on her ex-sempai Setsuna, but as time passes, she becomes really, *really*, creepily obsessed with Setsuna.
- Russia of \'\'Axis Powers Hetalia\'\' Used to Be a Sweet Kid then he became Cute and Psycho with Yandere tendencies for Japan and Lithuania.
- Manami Anzai from \'\'Life\'\', who first appears as a cute and childish click leader who snaps utterly when she suspects Ayumu is trying to steal away her boyfriend. She goes so insane that she then dates a gang leader on the side to use him to get back at both Ayumu and her boyfriend, and then promptly screws her boyfriend and the gang leader both over. Not to mention her vow to kill Ayumu with her bare hands. Then she crosses into Cute and Psycho territory.
- Lydia of \'\'Caught In The Act\'\' (by Peter Moore) is an outcast new at Ethan\'s school who develops a crush on him. Seems like a normal goth girl until she starts acting increasingly unstable and she ends up trying to have him killed after he tells her that he is not dating her.
- Debbie of \'\'Devil In The Flesh\'\' starts off with having a school girl crush on her teacher, becomes a Stalker with a Crush for him, and ends up killing people and trying to kill her teacher\'s wife.
- Alex of \'\'Fatal Attraction\'\' has a one-night stand with Dan and seems fairly normal but becomes increasingly more unhinged and unstable as Dan continually rejects her. She ends up trying to Murder the Hypotenuse and boils a bunny in a pressure cooker.
- Beauty and the Beast: Gaston increasingly goes from being a Jerkass Stalker with a Crush into a murderous Yandere through the course of the movie. It's especially evident after Belle keeps refusing him.
Gaston: I'll have Belle for my wife! Make no mistake about that!
- In Swimfan Madison initially doesn't seem all that upset that her one time lover Ben has a girlfriend Amy already but then she becomes more unhinged and tries to murder Amy...
- \'\'P!nk\'\' in the music video for \"Please Don't Leave Me\". She starts off being portrayed as a standard issue The Woobie Tsundere trying to keep her boyfriend from dumping her. Until he slips on marbles at the top of the stairs. The robotic head tilt she does looking down on him pretty much seals it. Madness, violence, and cute little hats ensue.
Hello, Unknown Troper. You'll need to get known to lend a hand here.