Mayo Chiki!, Manga Book 4

Kinjiro Sakamachi is a "normal" seventeen-year-old boy who happens to suffer from an abnormal fear of women, otherwise known as gynophobia. A fateful visit to the school bathroom turns Kinjiro's world upside down, as he discovers the dashing and popular Konoe Subaru is actually a girl!
 
Mayo Chiki!, Manga Book 4, Like New