Undertale au concept: it's an alternate timeline like dr is, but ut!chara is there. the story progresses as Chara is given more and more time to reflect and have a character arc. (this would be under the "Chara is somebody with issues" umbrella rather than the "Chara was always a psycho murder bastard that likes to kill people complexity who?" umbrella. by following the perspective of Chara, we slowly can find a way to help them as they are the only unsavable character in undertale.