秘蜜〜聖戦の誓い〜 (Himitsu ~Seisen no Chikai~)

Background
This song is part of the Himitsu series. It was released on the Polkadodge album.

This song tells of the war that took place over a thousand years before the events of Oath of Black. Kaito, the angel queen Lily and and a green haired angel(Mikuo) fought a demon to protect "the holy Eden" and banished him to the earth.