Kiichirō Miki is a twenty-six-year-old system engineer whose coworkers see him as expressionless, dull, and completely uninteresting. At company drinking parties he stands apart and appears to have no fun at all. But his younger sister, Miki, who lives in the apartment next door and spends nearly every day in his room, knows the truth. By night, Kiichirō is the legendary postcard craftsman Fruit Parfait, a radio listener whose witty and inventive postcards to the program All Night Nippon are frequently read on air and admired by fellow listeners. Only his sister is aware of this secret identity, and she considers her brother the most interesting and kindest person in the world.

The series follows the daily life of this reserved pair. Miki is a popular idol in the group xoxo, known to fans as Mikimiki, and shares her brother’s stoic exterior. At home, she is lazy and relies on Kiichirō for comfort and care. Kiichirō’s humor, which he channels into his radio postcards, was originally honed to make his baby sister laugh, and he continues to send her daily unreleased gags through a private social media account to cheer her up during her idol career.

As the story progresses, Kiichirō’s hidden qualities begin to draw a small circle of people who come to understand him. His coworker Hirose Sumine, a gentle woman trapped in a difficult relationship, notices his quiet thoughtfulness and starts to develop feelings for him. The stern section chief Yokoo Tsubomi, feared as an office tyrant, turns out to be a devoted fan of the same radio show and recognizes Fruit Parfait’s distinctive style, becoming a fellow enthusiast. Another postcard craftsman, Momi Tiger, reaches out to Kiichirō as a kindred spirit, giving him his first friend from outside the office.

Through these relationships, Kiichirō’s world slowly expands from the narrow circle of just his sister to include coworkers and fellow radio fans. The narrative blends gentle comedy rooted in misunderstandings about Kiichirō’s blank expression with warm moments of sibling affection and the gradual, understated growth of his social life. Notable story arcs include the first contact between Miki and Hirose, the discovery of Yokoo’s secret fandom, the sibling bond tested as others begin to appreciate Kiichirō, and a company trip to Okinawa where Kiichirō quietly helps a colleague considering a job change. The manga maintains a low-key, humorous tone, focusing on the small, funny, and touching moments of everyday life.