"My Little Monster" centers on the unlikely relationship between Shizuku Mizutani, a studious and emotionally detached high school student, and Haru Yoshida, a volatile and socially isolated classmate. Shizuku prioritizes academic success above all else, maintaining a cold demeanor that keeps her peers at a distance. Haru, on the other hand, is known for his erratic behavior and frequent absences from school, earning a reputation as a troublemaker. Despite their contrasting personalities, their lives intersect when Shizuku is tasked with delivering class materials to Haru, sparking an unconventional bond.

Haru becomes infatuated with Shizuku, declaring his feelings for her almost immediately. His unfiltered honesty and unpredictable nature challenge Shizuku’s rigid worldview, forcing her to confront emotions she has long suppressed. As their relationship develops, the story explores themes of friendship, love, and personal growth. Shizuku gradually opens up to Haru and others, while Haru learns to navigate social norms and control his impulsive tendencies. The narrative also delves into their interactions with classmates, including Haru’s childhood friend, Yuzan, who harbors complex feelings about their relationship, and Shizuku’s friend, Asako, who provides a more grounded perspective.

The manga balances humor and heartfelt moments, depicting the awkwardness and sincerity of adolescence. Shizuku’s pragmatic approach to life contrasts sharply with Haru’s chaotic energy, creating a dynamic that drives both comedic and emotional scenes. Secondary characters, such as the kind-hearted Sasahara and the mischievous Oshima, add depth to the story, highlighting the challenges and joys of forming connections during high school. Through its exploration of relationships and self-discovery, "My Little Monster" presents a nuanced portrayal of young love and the complexities of human interaction.