"High School DxD" centers on Issei Hyoudou, a second-year high school student with a penchant for perverse thoughts and a dream of building a harem. His life takes a dramatic turn when he is killed on his first date by a fallen angel named Raynare, who poses as his girlfriend. Revived as a devil by Rias Gremory, a high-ranking devil and president of the Occult Research Club at Kuoh Academy, Issei becomes her servant and joins her peerage. The series explores his journey as he navigates the complex world of devils, angels, and fallen angels while balancing his newfound responsibilities and personal desires.

Rias Gremory, the heiress of the Gremory clan, is a powerful devil who leads her peerage in battles and political conflicts within the devil hierarchy. Her peerage includes Akeno Himejima, her loyal queen and childhood friend; Koneko Toujou, a quiet and reserved rook; Yuuto Kiba, a skilled swordsman and knight; and Gasper Vladi, a reclusive vampire bishop. As Issei grows stronger, he forms close bonds with his fellow peerage members and develops romantic feelings for Rias, though his interactions with other female characters often lead to comedic and awkward situations.

The narrative delves into the power struggles between the three factions—devils, angels, and fallen angels—while also introducing other supernatural beings such as dragons, gods, and mythical creatures. Issei’s latent potential as the host of the Red Dragon Emperor, Ddraig, becomes a focal point as he trains to harness his abilities and protect those he cares about. The series balances action-packed battles, comedic moments, and romantic tension, often highlighting Issei’s growth from a lecherous teenager to a more mature and determined individual.

Key story arcs include the Rating Games, a competitive system where devil peerages battle for prestige and influence, and the conflict with the Khaos Brigade, a rogue organization seeking to overthrow the existing supernatural order. Throughout the series, Issei faces formidable opponents, uncovers hidden truths about his powers, and strengthens his relationships with Rias and the other members of the Occult Research Club. The narrative also explores themes of loyalty, ambition, and the complexities of love within the framework of a supernatural high school setting.