In the distant past, a war between humans and demons brought about widespread chaos and bloodshed. To put an end to this seemingly endless conflict, Demon King Anos Voldigoad willingly sacrificed his life, hoping to be reborn in a peaceful future. In preparation for their king's return, the demon race created the Demon King Academy, an elite institution tasked with determining Anos' identity when he reawakens. He reincarnates two millennia later, but to his surprise, he soon learns that the level of magic in the world has drastically waned during his absence. Moreover, when he enrolls at the academy to reclaim his rightful title, he finds out that demonkind remembers him differently. His personality, his deeds, and even his legacy are all falsified—masked beneath the name of an impostor. This "lack" of common knowledge renders him the academy's outlier—a misfit never before seen in history. Despite these drawbacks, Anos remains unfazed. As he sets out to uncover those altering his glorious past, he takes it upon himself to make his descendants recognize that their ruler has finally returned.

"Show them your A-O face!" As an innocent child, Ao Horie would unhesitantly proclaim the origins of her name. Now that she is in high school, she is determined to study hard in order to one day escape the influence of her lascivious father, a famous erotic author. However, when the amiable Takumi Kijima confesses to Horie, her mind runs wild with scandalous thoughts. Moans eager to escape, legs crossing, and a warmth spreading through her body, Horie cannot help but misconstrue Kijima's rather pure motivations. To make things worse, no matter how hard she tries to ward off Kijima, his advances do not stop. Now, if only she could just study!

For generations, the Bernstein family has been recognized as a house of nobles who favor books over everything else. Elianna Bernstein, daughter of a baron of the Sauslind Kingdom, is no different. But instead of being called a bookworm, she is known as the Bibliophile Princess. Four years ago, the crown prince, Christopher Selkirk Asherald, offered Elianna a special arrangement: if she would become his fiancée, he promised that she could continue to spend all her free time reading. Despite having to inherit a title of great responsibility, she agreed to the proposal, enticed by the prospect of gaining access to the royal archives housing a wide selection of books. To this day, Elianna firmly believes that her engagement is void of romantic sentiment. When she notices Christopher's interactions with another girl, she presumes that the days she spends with him will soon reach an end. Yet, during this period of uncertainty, Elianna and Christopher open a new chapter in their relationship, gradually uncovering their genuine feelings as they grow to better understand each other.

Manji is an infamous swordsman in feudal Japan who is known as the "Hundred Man Killer," as he has killed one hundred innocent men. However, there is something far more frightening than his ominous reputation: the fact that he is immortal. This is the handiwork of eight-hundred-year-old nun Yaobikuni, who placed bloodworms capable of healing almost any wound in Manji's body. To atone for his crimes, Manji resolves to kill one thousand evil men. Yaobikuni agrees to this proposal, saying that if he succeeds, she will undo his curse of immortality. Soon after this promise, Manji meets Rin Asano, a 16-year-old girl who requests Manji's assistance in killing those who slaughtered her parents. Initially reluctant, Manji refuses Rin's desperate plea. However, owing to her evident lack of strength, Manji changes his mind and agrees to protect Rin for four years. With this partnership set in stone, the two embark on a perilous journey of bloodshed, vengeance, and redemption, each to fulfill their own life's cause.