I enter the Ark of Yamato, leaving Issun behind as he had both finished copying all Amaterasu’s Brush Powers and was barred from entry regardless, and fight all the boss demons that we had defeated previously (excluding Lechku & Nechku).

It makes perfect sense for there to be a boss rush in this game, as the bosses had never been truly killed but simply driven back to the Ark; it doesn’t make it any less annoying, though.