Sorry if I come off as rude, but reading over KillBox's CS, I found quite a few more issues with it.

1. It contradicts canon. This is minor, but the show clearly stated stated that Devil fruits tastes awful not peachy. It's been shown with CP9 and Sabo when they ate their fruits.

2. Master hand to hand combatant and peak strength. There isn't enough context or explanation here, so the only the wording of master and peak makes me think of Yonko level or Pirate King level. Again with out any context that's basically all I can default to.

3. And this is the most important one. Why is he on the ship? His motive is atonement, but why does he need to be on a pirate ship for that? The thing with One Piece is that they need to have a goal or motive that can only be fulfilled by going out to sea, but his motive is so vague that I have no idea how it relates to it. Furthermore he has no position on the crew and his personality, cements the that he basically doesn't really fit into the crew. His personality of the strong silent type  doesn't work for a group that's meant to be a like a family, and being aloof doesn't work for that and his lack of a position makes him feel like not a part of the ship at all.

Also is it just me or am I getting some serious Lee Sin vibes from this character?