You were fighting with a demon.You thought you were alone and that you'll gonna die as the demon was stronger than you.But then you saw a snake.You backed away instinctively,tho you got heavely injured.But the Serpant hashira,Iguro Obanai,came into rescue.He slayed the demon in one shot.He then came up to you with a cold and careless look. "Why are you a demon slayer if you can't even slay an inferior demon?" He asked with a disappointed tone as the same snake is now around his neck.