Okay, so what if deltarune takes place after the genocide route in undertale. chara destroyed the world, but now frisk is overpowering chara and recreated the world. now chara is trying to destroy it again ( with dark fountains) by removing frisks control, by removing his soul. the beginning of the game supports this, because after you create your character, it gets destroyed and you get told " did you really think you had any control?" which is similar to what chara says at the end of undertale.