So basically, there's this person called Chara, they hate humans. They fall down the same hole frisk falls down later. Asriel, the son of toriel and asgore helps Chara get to his house. Chara makes Asriel feed her buttercups to kill them and bring their corpse to the human village. Asriel, after absorbing the human soul can pass the barrier, but the humans hurt him real bad. He manages to go back through the barrier but turns to dust on the flowers. Now with both of his children dead, Asgore decides to kill every human that ever falls down. Toriel divorces Asgore and he has to move out and make new home. Dr. Gaster tested determination extracted from human souls on a flower, coincidentally earlier covered in Asriel's dust, making flowey, who's a reincarnation of Asriel. Checkmate