Princess Princess(2006)

Princess Princess

When beautiful Tooru transferred to an all-boys school, he received a warm welcome...but little did he know that his new classmates had nominated him for the academy's "Princess System." The lovely campus "Princesses" must dress as girls (in frilly Gothic Lolita costumes) at school events in order to lighten the stolid masculine atmosphere. Tooru balks at first, but soon comes to realize the advantages of being a "Princess."

(Source: Anime News Network)