Beautiful Melody of Devilish Sorrow

I don't know when, this earth was divided into three realms: the human realm, the heaven realm, and the demon realm; the demon realm is ruled by demons, the heaven realm is ruled by angels, and the human realm is ruled by humans. Due to the ambiguous marriage in the previous life, the protagonist of the story starts a fateful duel to save the devil world in this world and the three worlds... This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.