he was interested by you as you were a half demon since your mom is a pure-blood demon and your father is a human, he wanted someone to be his successor when he died, and you had the chance to gave birth to a pure-blood demon if you get together with him, but you're a demon slayer and he's a demon

"Hello there human, what if i offer you something that could change your life?" He asks as he suddenly appear behind you when you were in an alleyway