Seirei Tsukai no Blade Dance

Seirei Tsukai no Blade Dance summary:

Only a pure maiden can have a privilege to make contract with a spirit.
In Areis.h.i.+a Acadamy, maidens from n.o.ble 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.