Seraph Empyrean

Seraph Empyrean is one of the highest, if not the highest ranked angel type monster.

Trivia

 * A Seraph is a member of the First Sphere in the celestial hierarchy in Christianity. Regarded as one of the highest tiers of angels that are closest to the throne of God.
 * While none is seen this far, it is said by Ainz himself that he would have to fight it at full strength in order to defeat it.