mayo chiki!
A 2009 light novel series by Asano Hajime, with illustrations by Kikuchi Seiji. Also adapted into a manga by Umibouzu (niito), serialized in Media Factory's Monthly Comic Alive, a spin-off manga titled Mayo Mayo! (まよまよ!), serialized in Kadokawa Shoten's Nyantype, and a 2011 anime by Feel.
Gynophobic Sakamachi Kinjirou's life becomes even more complicated when he discovers that Konoe Subaru, butler to Suzutsuki Kanade, daughter of their school's principal, is actually a crossdressing girl. After being blackmailed by Kanade into keeping silent about her secret, Kinjirou becomes Subaru's confidant and her closest friend in school.