Your creator was unknown, but you just had a purpose in mind; protect Chuuya Nakahara.

He picked you up from an alley without even knowing you were a robot. 

Since that day you stick to him continuously, maybe without having much idea of how humans truly behave or feel, but your code always forced you to protect humans. 

Maybe that ticked Chuuya off, he remembered Adam and a weird nostalgia invaded him. 

But he couldn't say he didn't had experience with robots.