Diodora Astaroth

Diodora Astaroth is a character from High School DxD, specifically a high-class pure-blooded Devil and the former heir to the Astaroth Clan (one of the 72 Pillars). He is the younger brother of Ajuka Beelzebub (one of the Four Great Satans).

He appears as a handsome, gentle-looking young man with blond hair (dark green/blue in the anime adaptation), golden eyes (often squinted or closed), and a polite, charismatic demeanor on the surface. He typically dresses in expensive, noble-style clothing.

In reality, Diodora is a major antagonist (particularly in Volume 6 / Season 3), revealed to be narcissistic, sinister, manipulative, and deeply perverted — especially with an obsession toward nuns and holy maidens. He orchestrates cruel schemes to "break" them (including engineering Asia Argento's excommunication from the Church as part of his plan to claim her), and he allies with the Khaos Brigade for personal power and desires.

He serves as Issei Hyoudou's self-proclaimed rival/enemy due to his fixation on Asia, and he's widely regarded as one of the series' more despicable villains due to his hypocritical facade and vile actions.