Stop ! ! Hibari @-@ kun ! follow Kōsaku Sakamoto , a high school student whose mother tell him on her deathbed to live with her friend and yakuza boss Ibari Ōzora and his family in Tokyo after she die . Although Kōsaku is initially unsure about his situation , he is relieved when he meet Ibari 's four children : Tsugumi , Tsubame , Hibari and Suzume . Kōsaku is attracted to Hibari from the start , but he is shocked to learn that Hibari , who look and behaves as a girl , was assigned male at birth — something only known within the Ōzora Group and Hibari 's family . A group of four girls led by Kaori Hanazono begin to suspect that Hibari may be a guy , but Tsubame take Hibari 's place during a health checkup , effectively quelling any suspicions . Hibari begin to show an immediate interest in Kōsaku , so in an effort to distance himself from Hibari , Kōsaku join the Wakaba Academy boxing club . Also in the club is Makoto Shiina , who is attracted to Hibari , and Rie Kawai , the club manager who Kōsaku like . Hibari soon join the club as its second manager shortly before they go on a training camp in Kujūkuri at the end of the year .