The Koshimizu-gumi was a Japanese yakuza organization that was affiliated with the Yomei Alliance of Onomichi, Hiroshima during the 2000s. The Koshimizu-gumi became the largest and most powerful organization within the Yomei Alliance under the leadership of Kanji Koshimizu, who became Heizo Iwami's handpicked successor. In 2016, the clan battled the Hirose-gumi (which was backed by Kazuma Kiryu) and kidnapped Kiryu's adoptive daughter Haruka Sawamura before the Hirose Family helped Kiryu recover her baby Haruto. After Tsuneo Iwami took charge of the Yomei Alliance, he had Koshimizu murder his father Heizo, and Koshimizu later kidnapped Kiyomi Kasahara to force Tojo-kai lieutenant Takumi Someya to battle of Kiryu. However, Koshimizu eventually broke with Tsuneo Iwami, refusing to kill Kasahara and instead releasing her back in Onomichi. Koshimizu eventually succeeded the arrested Tsuneo Iwami as chairman on his arrest, and the Koshimizu Family became the Yomei's main family to which all others rendered tribute.