Yandere-chan is a visual novel created with the free-to-use Ren'py engine. As the name implies, the main heroine of Yandere-chan is a Yandere of a truly epic proportion. The game begins when you transfer into a new school and meet a girl named Mia, who seems to know you. It only goes downhill from there. There is only one good ending in the entire game, all other endings end . . . messily.
Absurdly Sharp Blade: Yes, while it is possible to kill someone with scissors, Mia makes it seem easy.
Adding Insult to Injury: The entire last fifteen minutes of the poison ending, arguably. While your character is on the floor, hemorrhaging blood from their orifices, demanding a motive and insisting Mia lied the whole time, Mia spends the time they have left coldly debunking their argument, thereby denying them a chance to know why she did it, all while proving she never uttered a single false word. Ouch.
Ax-Crazy: Mia turns out to be this. In the good ending, she's getting better.
Berserk Button: Mia does not like it when you wash your blood off her calculator. Or get her name wrong.
Blatant Lies: After Mia fatally poisons you and your friends, you try and identify a moment when she did this. She never did.
Crazy-Prepared: Mia, during the second day. She prepared a lunch for herself because she was anticipating you asking her to sit with you at lunch; she also made poisoned raviolis in case you asked her to sit with you and your friends, with an extra container (to serve the non-poisoned pasta in) just in case.
Dull Eyes of Unhappiness: Mia, whenever her more 'emotional' side is about to rear its head. Actually Lampshaded by the player character in a certain ending, where he actually checks his watch to see if it's after sunset because the highlights have left Mia's eyes. The distraction gets him stabbed.
If I Can't Have You: An essential for any Yandere's repertoire. When you want to spend time with your friends, depending on your choices, Mia will either kill you and herself, to get away from distractions, or poison you and your friends, then watch as you die in agony.
Perfect Poison: Aversion during the ravioli/poison ending; the victims are all portrayed as having extremely violent physical episodes, and the scene lasts for a good 20 minutes, but given Mia's... nature... it's likely she wanted to see them suffer horribly.