Well, despite the fact that they used "-kun" in the first chapter, the character has appeared very feminine, so I think it would be more surprising for someone to think Mameyama is a guy.
I'm a little surprised too, since Mameyama looks feminine to me. The androgyny is definitely on purpose though. @GodGinrai The kun in the first chapter actually isn't masculine, it's the "senior formally referring to a junior" kun being used as a joke.
@Denji Yea, that's how I interpreted it. I only mentioned the -kun, because it seemed like it could have been part of the reason some people thought Mameyama was a guy.
Well, you can only get appendicitis once I'd imagine. If only using too much magic didn't also give her the runs, I'd say she was able to unleash unlimited power now. Hard to have an epic magic showdown if it makes you shit your pants.