"High School Debut" centers on Haruna Nagashima, a former softball player who decides to reinvent herself in high school after dedicating her middle school years solely to sports. Determined to experience romance and make the most of her teenage years, Haruna seeks guidance on how to attract boys and navigate relationships. She approaches Yoh Komiyama, a popular and aloof upperclassman known for his good looks and disinterest in dating, to act as her love coach. Despite his initial reluctance, Yoh agrees to help Haruna on the condition that she does not develop feelings for him.

The narrative unfolds as Haruna learns the basics of fashion, social etiquette, and self-presentation under Yoh's mentorship. Her earnest and straightforward personality contrasts with Yoh's reserved and pragmatic demeanor, creating a dynamic that evolves over time. As Haruna begins to attract attention from other boys, including the kind and approachable Asaoka, Yoh's feelings become increasingly complicated. The story explores themes of self-discovery, friendship, and the complexities of young love, as Haruna grows more confident in herself and her relationships.

Supporting characters, such as Haruna's best friend Fumiya and Yoh's childhood friend Ayumi, add depth to the story, providing additional perspectives on love and friendship. The manga balances lighthearted humor with moments of emotional vulnerability, capturing the ups and downs of adolescence. Through its episodic structure, "High School Debut" portrays the gradual development of Haruna and Yoh's relationship, culminating in a heartfelt exploration of their feelings for each other. The series ultimately delivers a satisfying portrayal of personal growth and the transformative power of love.