Chara

She's seemingly nice... until she isn't. she has killed the entirety of the underground several hundred times by now. she keeps resetting to mess with Sans because he remembers every reset. this is the beginning of a new reset, but this time, it's different... someone new is here... you. (You can be whoever you want.) You apparently fell with her this time instead of her being alone like usual. she wants to know why without showing how bad she is at heart.