The story follows Iruma Suzuki, a 14-year-old human boy, who is sold to a demon by his parents. The demon, known as Sullivan, takes Iruma to the Demon World and officially adopts him as his grandson. He enrolls Iruma in the Babyls School for Demons where he is the headmaster and where Iruma quickly befriends the demons Alice Asmodeus and Clara Valac. However, Sullivan tells Iruma to never reveal that he is human since he will be eaten if anyone finds out. Iruma then vows to blend in during his time in the demon world, although he only stands out because of all the situations and adventures that arise.

Rishe Irmgard Weitzner finds herself in a familiar situation: her fiancé is publicly breaking off their engagement, and her ducal family is about to disown her in shame. However, Rishe is not distraught; she has already had six chances to rebuild her life and chase a different passion each time. But she would always get swept up in a war and die, so now she wishes for her seventh reincarnation to be easygoing and uneventful. What Rishe does not take into account is the presence of Arnold Hein, the crown prince of the Galkhein Kingdom. He is destined to usurp the throne and become a tyrant who starts a large-scale invasion of neighboring countries. To make their encounter worse, Arnold is the one who killed Rishe in her previous life. That is why it is all the more shocking when he proposes to Rishe on the spot. In pursuit of her desired life, Rishe must consider accepting Arnold's proposal and discover the reasons behind his brutal actions to stop the war from ever happening.

Following the conclusion of the three-way organizational war, government bureaucrat Ango Sakaguchi recalls an event that transpired years ago, after the death of the former Port Mafia boss. Osamu Dazai, still a new recruit at the time, was tasked with investigating rumors related to a mysterious explosion that decimated part of the city years ago—and its connection to the alleged reappearance of the former boss. Due to circumstances out of his control, he is partnered with Chuuya Nakahara, the gifted yet impulsive leader of a rival clan known as the ''Sheep,'' to uncover the truth behind the case and shine a light on the myth of Arahabaki—the god of fire who might just lead Dazai to the case's solution. Meanwhile, in the present day, it is business as usual once again for the Armed Detective Agency. Their peaceful break will not last for long, however, as enemies old and new gather their strength and prepare for another face-off. [Written by MAL Rewrite]

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. [Written by MAL Rewrite]