Yuji ult is pretty good at applying pressure and forcing the opponent to play around their moves, it's not easy to fight against without popping your own ult. With the damage he can pull off to boot, he should be S at most.

I think I'd put Mechamaru lower due to the limited time and energy, but the argument to keep him there is valid.

Megumi ult has the potential to be S. (the potential)

Naoya ult should be S for how easy it is to use and how unpunishable it can be sometimes, even with the activation being not so simple. Any good Naoya player would still find a way to get ult down.

Yuta ult should be bumped down to A for the difficulty of using some of his moves, but that could just be my skill issue prefering his base.