Yamato from Megaton has a cool robot and he can actually fight rather well in his human form. It’s no exaggeration to say that he’s one of the more competent human kids out there. Still, he’s not quite ready to be dealing with Yamato from One Piece yet. Her abilities were enough to take on a Yonkou and she has an evolved state. With her speed speed and power this fight will be quick. Yamato wins.
Suggested by DMG Boa Hancock is strong enough to have been one of the pirates acknowledged by the world government. She should not be underestimated but Yamato was able to stalemate a Yonkou for a significant amount of time. There are few fighters in the entire verse who could have pulled that off. For this reason I do not think that Boa would stand much of a chance here. Yamato is stronger and I dare say that she is faster as well. This does not leave Boa a whole lot of options and her stone ability won’t be doing anything here. Boa would need a significant powerup to stand a chance. Yamato wins.
Yamato is a very powerful One Piece character but a very strong case can be made for Luffy being stronger still. His speed and abilities all appear to be greater than that of Yamato’s. In addition, Luffy’s devil fruit ability is just way too versatile to be beaten. He can shift gears at will and while I see this as an extremely close battle right now, it will probably become far less so as the years go on. Luffy will continue to get stronger. Luffy wins.
Tsumugi returns but is she ready to fight the warrior who even surpassed the lead performers? Yamato’s skill with a club is considerable and while Tsumugi does have some good speed moments of her own, they aren’t quite on the same level. She won’t be able to keep up with Yamato for long. Yamato is also more skilled so at the end of the day that is game over for Tsumugi. Yamato wins.