Mahou Senshi Sweet Knights: Heroine Ryoujoku Shirei

A subterranean magical realm called Roa, hidden deep within the Earth, is embroiled in a conflict between Queen Gloria's all-female knight corps and the monstrous forces of the evil syndicate Zerou. Metzer, a young and capable Zerou officer, receives authorization from his superiors to enact a personal strategy. He is covertly dispatched to the surface world to befriend the Sweet Knights, two Japanese girls empowered by Queen Gloria to defend Earth from syndicate monsters. His objective is to identify their vulnerabilities, then use his creatures to overpower, capture, and mentally reprogram them into obedient sex slaves for Zerou. The syndicate remains unaware of Metzer's own expansive ambitions for the time being.