聖骨のセバスティアヌス

Ira's true identity is Sebastianus of the Holy Bone, an apostle of Index. In 1945, he lost his life trying to commit a double ******* with the witch Lieselotte Werckmeister, but failed. 
Sebastianus was resurrected as Ira, remembering nothing but his mission to protect the seal. 

11eyes wiki.