Shounen-in Ushijima-kun

An official spin-off about Ushijima's past! The main character is young Kaoru Ushijima, who had not yet encountered black finance, in the winter of his second year of junior high school. Following his conflict with the three Wanido brothers, he swung a metal bat at Sanzo's head. Taken to a juvenile detention center on charges of causing bodily harm, what will Ushijima think about his first time at a place like this?

(Source: Shogakukan, adapted & translated)