How My Cousin Tricked Me into Becoming a Board Duck in the Apocalypse

First, the apocalypse arrived. But it's no big deal. I know martial arts. I don't know how to use supernatural powers, but body enhancement is all I need. Then there's the problem: I have a cross-dressing younger brother. He has the same ability as me, and he figured out how to use it.

He turned into Seele, then got me turned into Bronya. But that's not the problem. The problem is, even before transforming, he was already obsessed with sword fighting me! Aaaaaah!