First life
She is a goddess, and he is just the abandoned son of the Demon Lord, trying to catch a leaf.
Second life
She is the God of War in the immortal world, and he is already the Demon Lord, but they fail to recognize each other.
Third life
They are brother and sister, she is the leader of the Demon Envoy of the Demon Execution Pavilion, and he is the deputy leader.
They fell in love with each other during their time together, but she only regarded it as a normal relationship between brother and sister, but he did not think so.
Concept: Monsters are not all evil, and humans are not all good.