The 1910s. Iwamoto Kodo, a student at Suho Junior High School under direct command of the army, is investigating paranormal phenomena across the country as per military instruction. In a village rumoured to have black snow, he meets a boy with special powers who believes them to be an illness; through Iwamoto's support, he realises they might have something in common and receives a recommendation to the school. Mysteries await Iwamoto at each place he visits–a romantic tale of this era begins to unravel! (Source: MAL News)

Kuroe Akaishi is an introverted, quiet, and seemingly normal high school girl. Though accustomed to being alone, her dreary days begin to change when she meets Arata Minami, a bright and handsome boy in her class. Despite his popular status, he is kind enough to reach out to an outcast like her; soon, Kuroe finds her heart begins to pound around him. It keeps pounding and pounding and pounding until Kuroe transforms into a monstrous kaijuu! She has a certain affliction: as her embarrassment grows, so do the monstrous appendages from her body; and when it hits a peak, she unleashes the full extent of her transformation. At the same time, beauty meets the kaijuu, and Japan faces off against the looming threat of the mysterious monster. Can Minami accept her feelings, or will he too be frightened off by her colossal form? Depending on his decision, the world may experience the full devastation of a girl's heart-pumping, youthful love.

Through their tutor Fuutarou Uesugi's diligent guidance, the Nakano quintuplets' academic performance shows signs of improvement, even if their path to graduation is still rocky. However, as they continue to cause various situations that delay any actual tutoring, Fuutarou becomes increasingly involved with their personal lives, further complicating their relationship with each other. On another note, Fuutarou slowly begins to realize the existence of a possible connection between him and the past he believes to have shared with one of the five girls. With everyone's feelings beginning to develop and overlap, will they be able to keep their bond strictly to that of a teacher and his students—or will it mature into something else entirely?

Fuutarou Uesugi's efforts as the Nakano quintuplets' private tutor are finally paying off. The academic performances of the five sisters are steadily improving, and they are each closer than ever to achieving their respective dreams. However, it appears that Fuutarou has become more than a teacher for the girls, who urge him to sort out his feelings. The undecided young man promises to make a decision by the end of the school festival. However, Fuutarou's task will not be easy, as the Nakano sisters pull out all the stops to win his heart before it is too late.