"Oppai Party" is a comedic manga series that revolves around the lives of a group of high school students who form an unconventional club centered around their shared appreciation for a particular physical attribute. The story primarily focuses on the protagonist, a shy and reserved male student who, after a series of awkward encounters, is reluctantly drawn into the club by its eccentric members. The club, officially named the "Oppai Party," is led by a charismatic and outspoken female student who is unapologetically passionate about their cause. Despite its seemingly frivolous premise, the club often finds itself embroiled in various school-related activities and challenges, which serve as the backdrop for both comedic and heartfelt moments.

The narrative explores the dynamics between the club members, each of whom brings a distinct personality and perspective to the group. The protagonist, initially hesitant, gradually becomes more involved in the club's activities, forming genuine bonds with the other members. The series balances humor with moments of character development, as the students navigate typical high school experiences such as friendships, rivalries, and personal growth. The interactions between the characters often highlight themes of acceptance, self-confidence, and the importance of finding one's place within a community.

Throughout the series, the club faces opposition from other students and faculty who misunderstand their intentions, leading to a series of comedic misunderstandings and conflicts. However, the members consistently demonstrate their dedication to each other and their shared interests, often turning these challenges into opportunities for growth. The manga maintains a lighthearted tone, with occasional forays into more serious topics, ensuring a well-rounded narrative that appeals to a broad audience. The characters' relationships evolve over time, with the series concluding on a note that emphasizes the value of camaraderie and staying true to oneself.