Atsushi Arisawa, nicknamed Akkun, enters Jougaoka High at sixteen, determined to reconnect with his childhood crush, Masami Shibata—"Ma-chan." A case of mistaken identity upends his plans when he confuses Masami’s younger brother, Masayoshi, for her due to their striking resemblance. Masayoshi’s bold, carefree nature clashes with Atsushi’s memories of Ma-chan’s gentleness, sparking initial turmoil.

A Tokyo native living with his parents and a dog, Atsushi balances academic skill with youthful naivety. Over years, his infatuation shifts from Masami to Masayoshi, fueling a quest to earn Masayoshi’s respect and affection. This journey traces his growth from an eager teenager to a self-assured adult, culminating in a career as a student teacher and later a full educator at an all-girls school.

His relationships weave complexity: classmate Kouji Inagaki nurses unrequited feelings for him, leading to awkward yet humorous exchanges, while Yoriko Hayase, a mutual friend, quietly pines for Kouji. At home, Atsushi’s warm, treat-baking mother contrasts with Kouji’s stern parent.

As Atsushi matures, so does his dynamic with Masayoshi. Once the submissive half of their pairing, he gradually asserts equality, mirroring his professional resolve. Their bond stabilizes into mutual respect, underscored by Atsushi’s determination to match Masayoshi’s emotional and career footing.

The OVA introduces an anime-exclusive twist—Atsushi’s kidnapping, resolved by Masayoshi and Kouji’s rescue—showcasing the series’ blend of comedy and tension. Meanwhile, interactions with Masayoshi’s family deepen his ties to the Shibatas: father Yoshiyuki, who warms to Masami’s romantic choices after initial resistance, and a grandmother whose approval comes with conditions, further anchoring Atsushi within their intricate familial web.