Kyou kara Maou! revolves around Yuri Shibuya, your average Japanese teenager. One day, Yuri sees a classmate being harassed by bullies. Thanks to this intervention, his friend is able to escape, but unfortunately Yuri becomes the new target of the bullies in the process and gets his head shoved into a toilet. But instead of water, the toilet contains a swirling portal that sucks him into another world, largely resembling medieval Europe. There, he is told that he will become the next Demon King due to his black hair and black eyes, traits only possessed by the demon's royal lineage. Yuri's arrival is met with some skepticism by some of the demons, who view him as unworthy to be their king. However, after Yuri wins a duel by utilizing his magical powers, the demons slowly begin to acknowledge him as their monarch. Yuri must now learn what it takes be a true Demon King, as he tries to keep the peace between demons and humans in this strange new realm.

Freshman Kaho Nikaidou is from an influential family, and as such, no one has ever said anything even remotely mean to her, for fear of incurring her household's wrath. Wishing to be around people who will not treat her as special because of her background, she leaves home to live at a dormitory for her new school year. Shortly after arriving, Kaho accidentally wanders into traffic and is saved by a tall, handsome stranger. When she asks for his name, he tells her she is weird and walks away. Having finally met the only person to ever say an unkind word to her, Kaho falls head over heels for her savior. After meeting her rescuer yet again and discovering that his name is Kanade Takahashi, she confesses her love to him. Kanade says he would like for them to be a couple, but that Kaho may not want to date him after she finds out his secret. To her shock, Kaho discovers the startling truth: Kanade is a fifth grader! Deciding that she can't date a fifth grader, Kaho intends to break up with him. But as she spends more time with Kanade, she begins to care for him even more and continues dating him. Hatsukoi Monster follows Kaho's first steps into love with Kanade, her immature, yet kind, fifth grade boyfriend.

Despite Kyouko Honda's tragic death, her vivid memory lives on, providing guidance through times of hardship to her close ones. However, Kyouko was not always the wise and radiant person that she is fondly remembered as in the present day. Feeling deserted by her own family and rejected by society, a young Kyouko abandons stability for a life of delinquency, jeopardizing her education and future. Fortunately, her descent into despair is interrupted by a fateful encounter with her husband-to-be Katsuya, who has recently started his teaching internship at her school. With a composure surprisingly unaffected by Kyouko's tantrums, Katsuya quickly wins her over through his gentleness and attention toward her—sincere gestures that she has never received before. As the two grow closer together, Kyouko opens her tormented heart to him and, along with it, a door to new horizons.

The king of Slantania has officially appointed Sei Takanashi as the Holy Saint—an omnipotent maiden summoned from another world to save the kingdom. After months of relentless fighting against monsters, Sei can finally relax and continue her study at the Medicinal Flora Research Institute. Although her relationship with Albert Hawke, the commander of the Third Order of Knights, gradually blossoms, her bachelorette status attracts unwanted attention from other men—much to Albert's dismay. Moreover, Tenyuu—one of the many princes from the faraway Zaidera Empire—has taken an interest in Slantania and its powerful healing potions. Given that Sei's identity is a national secret, she must lay low in the royal palace until Tenyuu satisfies his curiosity at the institute and returns to his country. Despite his unimpressive appearance, the foreign prince is far from clueless. He has come to Slantania for a clear reason, and Sei's unique skills may just hold the answer to his cryptic research.