Set in 1966, "Kids on the Slope" centers on Kaoru Nishimi, a reserved and academically gifted high school student who has moved frequently due to his father’s job. Arriving in Kyushu, Kaoru struggles to adapt to his new environment and feels isolated due to his introverted nature. His life takes a turn when he meets Sentarou Kawabuchi, a rebellious and impulsive classmate with a passion for jazz drumming. Despite their contrasting personalities, the two form a bond through their shared love of music, particularly jazz. Sentarou introduces Kaoru to the world of jazz, sparking a transformation in his outlook and helping him break out of his shell.

The story explores the evolving friendship between Kaoru and Sentarou, as well as their relationships with other key characters. Ritsuko Mukae, the daughter of a record shop owner and a childhood friend of Sentarou, becomes a central figure in their lives. Her calm and supportive demeanor provides a stabilizing influence, though her feelings for Sentarou add complexity to the dynamics between the trio. As the characters navigate their personal struggles, the narrative delves into themes of identity, belonging, and the power of music to connect people.

The plot unfolds against the backdrop of societal changes in 1960s Japan, touching on issues such as class differences, family expectations, and the lingering effects of World War II. Sentarou’s troubled family life, including his strained relationship with his stepfather, contrasts with Kaoru’s more privileged but emotionally distant upbringing. Ritsuko, meanwhile, grapples with her own aspirations and the weight of her family’s expectations. The series balances these personal conflicts with moments of joy and camaraderie, particularly during the characters’ jazz performances, which serve as emotional high points.

As the story progresses, the relationships between Kaoru, Sentarou, and Ritsuko grow more intricate, with moments of tension and reconciliation. The narrative builds toward a climactic performance that underscores the transformative impact of their shared experiences. Through its exploration of friendship, music, and self-discovery, "Kids on the Slope" presents a heartfelt and nuanced portrayal of adolescence, set to the rhythm of jazz.