Just in case you are not familiar with Yandere Simulator yet (in which case, you are missing out), let me sum things up for you. Yandere is a Japanese term that defines a very special kind of personality: what seems like an affable and good-natured person at first sight but actually has a very dark side with obsessive traits that might lead to violence.
The protagonist of this crazy stealth game is a Yandere-girl very originally named Yandere-Chan. She is madly (literally, you’ll see) in love with an older boy from her high school, her Senpai. The main problem is that Senpai doesn’t even know that Yandere-chan exists, so she comes up with the most logical of strategies: She decides to “slyly” kill every other girl from her high school so that Senpai has no option but to finally fall in love with her. It's the typical plan in which nothing can go wrong.
The player’s mission is to perform this madness of a setup and make sure that no one notices what is really going on: clean the blood, burn the bodies, go to class . . . that’s the daily routine of a Yandere girl. Ultimately the goal of the game is, of course, getting Senpai’s love, but for the time being, he will think of you as a creep. Who would blame him?