In a ritual, the Goddess bestows upon 10-year-old children a "class" that shapes their entire future. As the son of the legendary Sword Princess Fara and Archmage Leon—two of the highest-ranked individuals in their respective classes—Arel seemed destined for greatness. Unfortunately, he is branded as classless and thus unable to naturally inherit any kind of specific skill. However, Arel soon discovers that he can replicate the abilities of any class he desires—though doing so demands significantly more effort than it does for the naturally gifted. Eager to test his unprecedented skills even more by finding stronger opponents, Arel sets out to defy the limits imposed upon him and prove that perseverance can surpass even divinely appointed talent.

High school first year Yuu Yuutani has always been a good girl, following the rules, helping out around her house, and generally going through life unnoticed. From afar, she reveres her upperclassman and the school's Public Decency Officer, Atori Mizutori, and desperately wants her attention. When she realizes that the best way to get Atori to notice her is to be a delinquent, she begins to dress differently: she dyes parts of her hair a bright red, wears clips on her ears to resemble piercings, and attaches jumbo erasers to her shoes to give them thicker soles. Despite Yuu's best efforts and even with the advice of her "natural born delinquent" friend Suzu Suzukaze, all of her plans to be a bad girl go awry. Still, Yuu manages to befriend Atori and pledges to spend as much time as possible together, not knowing there are others vying for Atori's attention. In the process, Yuu has also gained the attention of the school's self-proclaimed idol, Rura Ruriha, filling her once-invisible life with more attention than she may be able to handle.

The story centers on Nayu, a middle school girl who shocks her schoolmates on the first day of school by wearing black lace panties. She likes this kind of underwear, and she tries to "spread the word on the merits of [these kinds of] underwear" via an underwear club with her schoolmates, who are worried about their bodies' development and which underwear to choose.

After Jinta and Suzune ran away from their home as children, they were taken in by Motoharu—the virtuous sentinel of Kadono Village—and his daughter, Shirayuki. The settlement was ruled by its shrine maiden, Itsukihime, whom only a select few were allowed to interact with. When Itsukihime passed away, Shirayuki was appointed in her place. Wishing to stay in contact with her, Jinta worked diligently for years and was finally selected as the next sentinel. As the protector of the village, Jinta's duty is to eliminate any threats. One day, he encounters a demon in a nearby forest. At the end of the battle, the demon makes a proclamation about the destined ruler of all demonkind. He attaches his severed arm to Jinta, turning him into an unaging demon man. By the time Jinta comes to, Kadono is on fire. Suzune has transformed into the demon from the divination, and due to a series of misunderstandings, she murders Shirayuki and flees. Devastated, Jinta cannot forgive Suzune for her actions; he departs on a journey to find her. As Jinta travels around Japan across the eras, he endeavors to protect as many people as possible from aggressive demons. In his quiet moments, he contemplates what he should do when he once again faces his childhood friend.