Thirty years ago, the Eurasian continent was devastated by a supermassive "spatial quake"—a phenomenon involving space vibrations of unknown origin—resulting in the deaths of over 150 million people. Since then, these quakes have been plaguing the world intermittently, albeit on a lighter scale. Shidou Itsuka is a seemingly average high school student who lives with his younger sister, Kotori. When an imminent spatial quake threatens the safety of Tengu City, he rushes to save her, only to be caught in the resulting eruption. He discovers a mysterious girl at its source, who is revealed to be a "Spirit," an otherworldly entity whose appearance triggers a spatial quake. Soon after, he becomes embroiled in a skirmish between the girl and the Anti-Spirit Team, a ruthless strike force with the goal of annihilating Spirits. However, there is a third party that believes in saving the spirits: "Ratatoskr," which surprisingly is commanded by Shidou's little sister! Kotori forcibly recruits Shidou after the clash, presenting to him an alternative method of dealing with the danger posed by the Spirits—make them fall in love with him. Now, the fate of the world rests on his dating prowess, as he seeks out Spirits in order to charm them.

High school student Issei Hyoudou is your run-of-the-mill pervert who does nothing productive with his life, peeping on women and dreaming of having his own harem one day. Things seem to be looking up for Issei when a beautiful girl asks him out on a date, although she turns out to be a fallen angel who brutally kills him! However, he gets a second chance at life when beautiful senior student Rias Gremory, who is a top-class devil, revives him as her servant, recruiting Issei into the ranks of the school's Occult Research club. Slowly adjusting to his new life, Issei must train and fight in order to survive in the violent world of angels and devils. Each new adventure leads to many hilarious (and risqué) moments with his new comrades, all the while keeping his new life a secret from his friends and family in High School DxD!

The misadventures of Issei Hyoudou, high school pervert and aspiring Harem King, continue on in High School DxD New. As the members of the Occult Research Club carry out their regular activities, it becomes increasingly obvious that there is something wrong with their Knight, the usually composed and alert Yuuto Kiba. Soon, Issei learns of Kiba's dark, bloody past and its connection to the mysterious Holy Swords. Once the subject of a cruel experiment, Kiba now seeks revenge on all those who wronged him. With the return of an old enemy, as well as the appearance of two new, Holy Sword-wielding beauties, it isn't long before Issei and his Devil comrades are plunged into a twisted plot once more.

The Red Dragon Emperor, Issei Hyoudou, and the Occult Research Club are back in action as summer break comes for the students of Kuoh Academy. After their fight with Issei’s sworn enemy, Vali and the Chaos Brigade, it is clear just how inexperienced Rias Gremory's team is. As a result, she and Azazel lead the club on an intense training regime in the Underworld to prepare them for the challenges that lie ahead. While they slowly mature as a team, Issei will once again find himself in intimate situations with the girls of the Occult Research Club. Meanwhile, their adversaries grow stronger and more numerous as they rally their forces. And with the sudden appearance of Loki, the Evil God of Norse Mythology, the stage is set for epic fights and wickedly powerful devils in High School DxD BorN!