Seventeen-year-old Rei Kiriyama lives alone in Tokyo's Rokugatsu-chō district, supporting himself as one of the youngest professional shōgi players in history. Orphaned as a child after a traffic accident killed his parents and younger sister, Rei was taken in by his father's friend, Masachika Kōda, a professional shōgi player who trained him in the game. The attention Rei received for his talent created deep resentment from his adoptive siblings, Kyōko and Ayumu, leading to a fractured and painful home life. After becoming a professional in middle school, Rei left the Kōda household to live in isolation, burdened by guilt and struggling with depression.

Rei's solitary existence begins to change when he encounters the Kawamoto sisters—Akari, Hinata, and Momo—who live in the neighboring Sangatsu-chō district. The sisters take him in after finding him collapsed and ill on the street, offering him the warmth and family connection he has long been missing. Akari, the eldest, works as a hostess in Ginza while helping her grandfather run a traditional Japanese confectionery shop. Hinata, the middle sister, is a strong-willed middle school student who develops a close bond with Rei. Momo, the youngest, is a cheerful preschooler. Their home, filled with cats and home-cooked meals, becomes a sanctuary for Rei.

The live-action adaptation spans two films released in March and April 2017, directed by Keishi Ōtomo. The story follows Rei as he navigates two contrasting worlds. One is the fiercely competitive and mentally grueling realm of professional shōgi, where he faces rivals such as Harunobu Nikaidō, a wealthy and chronically ill player who declares himself Rei's lifelong rival, and the powerful Kai Shimada, an eight-dan player from the countryside who mentors Rei. He also contends with the intimidating Masamune Gotō, a nine-dan player involved in a complicated relationship with Kyōko, and the silent and enigmatic Tōji Sōya, the reigning Meijin champion. The other world is the Kawamoto household, where Rei learns to accept kindness and confront his own emotional wounds.

A significant narrative arc involves Hinata Kawamoto, who becomes the target of severe bullying at her middle school. Drawing on his own painful past, Rei supports her through this ordeal, and his determination to protect her deepens their relationship. Meanwhile, Rei continues to grapple with his complicated foster family, particularly his manipulative foster sister Kyōko, who resents him yet remains drawn to his orbit. Through his shōgi matches and his growing connections with the Kawamoto sisters and other players, Rei slowly begins to find a sense of belonging and a reason to live beyond the shōgi board.