HameKoi!

Most people have a secret they just can't tell others.
For me, I have two. I have someone I like, and the other is...

I am crossdressing while attending an all-girls' high school.

I, Mizuki Saiki, have an older twin sister named Miyuki: and to suit her own purposes, she is practically forcing me to crossdress, so that I can attend her all-girls school as a female student in her place.

"This way, I can stay together with my beloved childhood friend Kaya-chan... as long as I don't get found out!"
Earnestly trying to hide the fact that he's the only boy in a place full of girls... This is a comedy about a heart-pounding mission that's swirling with ulterior motives!

(Source: Gangan Online)