Seirei Tsukai no Blade Dance by Yuu Shimizu

Translated from Japanese Action Comedy Fantasy Romance Supernatural School Life Military Harem Magic Ecchi Royalty Loli Cross-dressing
Only a pure maiden can have a privilege to make contract with a spirit.
In Areishia Acadamy, maidens from noble family were gathered there, giving them an elite education to become a spirit contractor. A boy Kamito, by an accident he peeped into a girl, Clair, who was taking a bath, and he even made a contract with spirit that she wanted.
Kamito was actually an irregular male spirit contractor, which should not exist.

1: Seirei Tsukai no Blade Dance