Complex sentence: Chara journeyed to the mountain because they actually hated humanity; they died soon after, with Asriel also being slain the same night when he attempted to return their body to the human world.
Split into simpler sentences: Chara journeyed to the mountain because they actually hated humanity. Chara died soon after, with Asriel also being slain the same night when he attempted to return their body to the human world.