For 500 years, the Taboo Emperor, Arthur Gaz, ruled the Gaz Empire with an iron fist and conducted inhumane experiments on his own people. But his reign came to an end five years ago, when mighty warriors—later known as the Eight Heroes—defeated him in a battle for the capital. His death ended the 300-yearlong war between the Gaz Empire and the alliance of six nations. In the present day, Tooru Acura is a former saboteur from the war who has difficulty settling into the peaceful world, as he cannot find a job where he can put his fighting skills to use. An opportunity appears before him, however, when he meets a white-haired Wizard named Chaika Trabant. With a coffin on her back, she is searching for the scattered remains of her father in order to give him a proper burial, and she hires Tooru and his adoptive sister Akari to help her. However, the six nations alliance, which have now formed the Council of Six Nations, dispatches Albéric Gillette and his men from the Kleeman Agency to pursue and apprehend the late Emperor Gaz's daughter—Chaika. With the shocking revelation of Chaika's identity, the Acura siblings must choose between helping her gather the remains of the tyrannical emperor and upholding the peace the continent strives to maintain.

The search for the remains of Emperor Gaz continues. Chaika still in search of knowing who she really is and what her purpose is. Similarly, the Red Chaika continues the search for the rest of Emperor Gaz's remains. The Gillette corporation continues the mission to catch every last Chaika. In their adventure they give a revealing account kept secret by the Emperor, which Chaika, Fredrica, Toru, and Akari decide to uncover. (Source: ANN, edited)

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!