User blog comment:DeathGodPrayer/Talk About What You Want!/@comment-80.181.161.110-20130914173106/@comment-1359322-20130928003718

The author made Irina an Angel because he wanted Issei's harem to have variation meaning not only Devils but from other species too. Do you think he'll even make Irina a Devil. For starters, the Evil Pieces and Brave Saints can't coexist, they used a different reincarnation system and if Irina does accept the Evil Piece, she'll become a Fallen Angel immediately after that. Also being an Angel is Irina's life purpose, why would she abandon that role. Hell in the preview of Volume 16, Irina is already researching for a method to have sex and give birth without selling.