Following their heroic efforts at Walter Park, the students of the misfit class return to Babyls Demon School after their summer vacation. What awaits them is not only adoration and admiration but also the shocking revelation that, in order to stay in the luxurious Royal One classroom, the entire class must be promoted to Dalet rank before entering the second year. As the Harvest and Music Festivals are right around the corner, there seem to be ample opportunities to rank up. Doing so will not be simple, however, as no class thus far has managed to accomplish such a feat. Hoping to give the misfit class a chance to achieve the improbable, the school appoints special tutors to aid in confronting the challenges that lie ahead. With his sights set beyond Dalet, Iruma Suzuki decides to take strides toward the goal of ranking up, starting with gaining acknowledgement from his special tutor: the short-tempered and selfish Bachiko Barbatos.

The rare and inexplicable Puberty Syndrome is thought of as a myth. It is a rare disease which only affects teenagers, and its symptoms are so supernatural that hardly anyone recognizes it as a legitimate occurrence. However, high school student Sakuta Azusagawa knows from personal experience that it is very much real, and happens to be quite prevalent in his school. Mai Sakurajima is a third-year high school student who gained fame in her youth as a child actress, but recently halted her promising career for reasons unknown to the public. With an air of unapproachability, she is well known throughout the school, but none dare interact with her—that is until Sakuta sees her wandering the library in a bunny girl costume. Despite the getup, no one seems to notice her, and after confronting her, he realizes that she is another victim of Puberty Syndrome. As Sakuta tries to help Mai through her predicament, his actions bring him into contact with more girls afflicted with the elusive disease. [Written by MAL Rewrite]

Kaede Komura is in love. After being seated next to the airheaded Ai Mie for the past three days, Komura cannot help but be attracted to his bespectacled classmate. Although he has yet to have a proper conversation with Mie, Komura dreams of the day when she will look his way. One day, Komura notices that his seatmate is not wearing her glasses, learning by questioning Mie that she forgot them and has a tendency of doing so. When he sees her struggle, a concerned Komura takes it upon himself to help his crush. As the boy offers his assistance to Mie day by day, her reasons for constantly losing her glasses slowly evolve from the answer she initially gave.

It is business as usual in the massive city of Orario, where legions of adventurers gather to explore the monster-infested "Dungeon." Among them is the easily flustered yet brave Bell Cranel, the sole member of the Hestia Familia. With the help of his demi-human supporter Liliruca Arde and competent blacksmith Welf Crozzo, Bell has earned the title of Little Rookie by becoming Orario's fastest-growing adventurer thanks to his endeavors within the deeper levels of the Dungeon. Dungeon ni Deai wo Motomeru no wa Machigatteiru Darou ka II continues Bell's adventures as he tries to bring glory to his goddess and protect those he cares about. However, various familias and gods across the city begin to take notice of his achievements and attempt to add him to their ranks. [Written by MAL Rewrite]