Flowey is the yandere of the protagonist in the 2015 indie game Undertale.
While Flowey is evil and wants to pursue his own goals, he actually has a strong attachment to the protagonist. In the Neutral and Pacifist Runs, he tries everything he can to make sure they don't leave him. For the Neutral Run, he gets rid of their old save file and attempts to save over the main character's death.
If you backtrack through the Echo Flower field in Waterfall before you leave, the second flower will speak in Toriel's voice with a concerned tone, before switching to Flowey's voice and telling the protagonist that Toriel forgot about them. However, this easter egg requires that you spare Toriel first, otherwise he'll just try to make you feel guilty for killing her.