Asriela Drimmurr and Chara Drimmurr.

They are half-siblings. That is, Asriel, a monster in the form of an anthropomorphic goat, is the princess of a dungeon inhabited by monsters driven there by humans. Chara, on the other hand, is the first human to fall into the dungeon, with a soul of determination and murderous tendencies. He was also adopted into the royal family by Asriel and his adoptive father, Thorigor, after his adoptive mother, Asgiel, abandoned the family after humans traumatized her daughter.