A Game Informer interview with ARMS producer Kosuke Yabuki and art director Masaaki Ishikawa had a very interesting question that was asked over halfway into the interview. At one point, the Game Informer crew ask them if Luffy from One Piece would be a possible character to add post-release. This is because Luffy has arms that extend, similar to the characters in ARMS. However, Yabuki’s response was simple. The universes are different, so it wouldn’t happen. The entire quote is below.
Can one of those characters be Luffy from One Piece? He seems like he would fit in that universe.
Yabuki: I guess now that you mention it, Luffy’s arms do extend huh? I didn’t really think of that. But unfortunately, the world of Arms and the world that Luffy lives in are different worlds, so I don’t think he will be in this game.