アルジェント -, Ashia Arujento)
Voiced by:Azumi Asakura ( 浅倉 杏美 - Asakura Azumi )
Sister Asia Argento (アーシア・アルジェント Āshia Arujento?) is a nun whom Issei met while in town. She is a girl with a gentle heart who possesses a divine Sacred Gear, "Twilight Healing" (聖母の微笑(トワイライト・ヒーリング) Towairaito Hīringu?, lit. "Smile of the Holy Mother"), in her body which is capable of healing the wounds of humans, Angels, Fallen Angels, and Devils alike (in the anime, Twilight Healing takes the form of two rings inserted through her middle fingers).
Early in the series, she was once under Fallen Angels' (led by Raynare) control, but after a certain turn of events, she became a Devil under Rias' control and transfers to Issei's class. Her rank among Rias' underlings is "Bishop". When Issei saved her from the Fallen Angels, she fell in love with him, and eventually with interventions from their leader Rias, moved in with him to live together at the Hyodo household. While the perverted side of Issei wants to do naughty things to her, his actual feelings towards Asia is a bit complicated, as he also sees himself as the protective guardian of the simple-minded, pure-hearted girl that Asia is, which in turn deters him from doing all the forementioned things to her that he fantasizes about. Asia has a baby Sprite Dragon as her pet and familiar whom she named Rassei, after Issei's name.
Despite being revived as a Devil, Asia stills believes in God and tries to read the Bible and constantly prays to God, which results in her getting severe headaches and was in shock when she found out that the God in the Bible is dead. However, Issei asked the Archangel Michael to let Asia and Xenovia pray to God without letting them suffer headaches when they do it.