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.

Twenty-six-year-old Hiroto Suwa; his wife, Naho; and their old high school classmates—Takako Chino, Azusa Murasaka, and Saku Hagita—visit Mt. Koubou to view the cherry blossoms together. While watching the setting sun, they reminisce about Kakeru Naruse, their friend who died 10 years ago. Mourning for him, they decide to visit Kakeru's old home, where they learn the secret of his death from his grandmother. Filled with regret, Suwa and his friends decide to write letters to their 16-year-old past selves to set their hearts at rest. With the knowledge contained in the letter from his future self, 16-year-old Suwa has the chance to rewrite the future. What choices will he make? What will happen in this new future? [Written by MAL Rewrite]

Haruka Kiyomine and Kei Kaname were once recognized as the most formidable pitcher-catcher duo in middle school baseball. Known as the "General," Kaname paired his expert strategies with Kiyomine's explosive pitches, crushing the dreams of many starry-eyed players who hoped to one day make it to the big leagues. High school freshman Tarou Yamada is one such former player. Having given up on competing, he enrolls in Kotesashi High School—a completely average public school with no baseball team to speak of—where he discovers that his new classmates are the legendary pair who once destroyed his dreams. Adding to this shocking revelation, he learns that amnesia has reduced the once level-headed General to a vulgar class clown. Having lost all interest in baseball, Kaname dragged a disappointed Kiyomine to Kotesashi simply because the school was close to where they live. As Kotesashi forms a fledgling baseball club, Yamada meets other players he once admired who also left baseball behind. While they might be unwilling now, Yamada believes that if he can convince such talented athletes to start playing again, it might be possible to achieve their dreams and win the national championship—as long as they can put up with Kaname's incessant joking.

The cheerful Yuuki Cross and the gruff Zero Kiryuu are members of the disciplinary committee at Cross Academy, which houses two very distinct classes: the Day Class and the Night Class. Their job consists of upholding order between the classes when they switch out. While that may not seem like an especially difficult task, the Day Class is unaware of the truth behind the Night Class—their utterly gorgeous students are vampires. Ten years ago, Yuuki was saved from a vampire attack by Kaname Kuran, a Pureblood vampire. Now, Kaname is the leader of the Night Class, and Yuuki's disciplinary committee position allows her to see him again, making her feelings for him grow complicated. Meanwhile, Zero bears a white-hot hatred of all vampires and believes they can never live in harmony with humans. But a secret from Zero's past soon threatens the fragile peace of all at the academy, and things may never be the same again. [Written by MAL Rewrite]