"Dasshu Kappei" centers on Kappei Sakamoto, a short-statured but highly energetic and mischievous high school student with a knack for getting into trouble. Despite his small size, Kappei is a skilled basketball player, using his agility and quick thinking to outmaneuver opponents. His life takes a turn when he meets Aoi Manami, a tall and athletic girl who becomes his love interest. Their relationship is marked by comedic misunderstandings and playful rivalry, as Kappei often tries to impress her with his antics, though his efforts frequently backfire.

The series blends comedy, romance, and sports, with much of the humor arising from Kappei's exaggerated personality and his interactions with the eccentric cast of characters. These include his classmates, such as the stoic and serious basketball team captain, and his overbearing mother, who often embarrasses him with her over-the-top behavior. Kappei's basketball skills are put to the test in various matches, where his determination and creativity shine, even when facing physically stronger opponents.

The narrative explores themes of perseverance, self-confidence, and the importance of teamwork, often through lighthearted and slapstick scenarios. Kappei's journey is one of personal growth, as he learns to balance his impulsive nature with the responsibilities of being a team player and a friend. The series maintains a comedic tone throughout, with occasional moments of heartfelt sincerity, particularly in Kappei's evolving relationship with Aoi and his efforts to prove himself both on and off the court.