Izumi, a college student, is asked out by a classmate, Yuuji, who was the hero of the baseball club in high school, and gets lost in a mysterious place. There was a mysterious market called the “Night Market” where youkai sell various goods and can get whatever they want. Yuuji had once wandered into this Night Market before as an elementary school student with his younger brother, where he had sold his younger brother for baseball talents. What is Yuuji's motive for coming to the Night Market once more? (Source: Akita Shoten, translated)

Yoichi is an adaptation of Koutarou Tsunekawa's short story of the same title.