I've read a manga some time ago about a boy transferring into a high school full of ninjas or special warriors of some sort. If I remember correctly, it was kind of an ecchi because he was surrounded by female ninjas...? It had a dark feel to it, most likely not a comedy. What's significant to my memory is that the story had a twist to it, where the love interest of the boy was the key (or something like that) to saving the world, or the illusion that everyone's been living in. It wasn't a very long manga, possibly around 15 chapters? I remember completing it.

This manga is almost nonexistent in my memory, but the twist is what made me suddenly remember it. Sorry for the unclear summary. Anyone know what manga i'm describing?

Don't know if its the one you're looking for, but the first manga that came to my mind from what you described was Yakuza Girl.

I was doubting it was Yakuza Girl at first, but that's exactly it! Thank you very much!