Demon Slayer: Kibutsuji Taibai

Taibai grew weary of the dangers and treachery of the human world. In a past life, he had once been a god and possessed a mysterious power called dark energy. He transmigrates to the world of Demon Slayer, and, unbelievably, his younger sister Xing Ling'er comes along too, after somehow crashing into a telephone pole.