Neo would have happily just gone about his life if his older sister didn't fall ill. He certainly wouldn't have gone to crime to try to find a cure for her when the doctors wouldn't do anything to try and remove her tumors. He also never expected his bestfriend to wind up as his nemesis nor stab him in the back- literally.

As he lays there, fading away, an otherworldly voice offers him a very lucrative deal: a second chance at life, another chance to save his sister at the cost of his soul and becoming a demon.

He took the deal anyways. He'd do what it takes to save her.