The Seiryu-kai was a Japanese yakuza clan which, as part of the Ijin Three, dominated Yokohama's criminal underworld during the 21st century. The Seiryu-kai was formed in the immediate aftermath of World War II and controlled most of the black markets in Allied-occupied Yokohama, as well as protecting local businesses from looters in exchange for protection payments. During the 1950s, a group of Chinese refugees founded the Yokohama Liumang, which became rivals with the Seiryu-kai. LDP politician Yutaka Ogikubo intervened to stop further escalation of the rivalry into a gang war, and the Seiryu-kai and Liumang partnered in a money counterfeiting operation masterminded by Ogikubo; the Korean Geomijul was later included in the arrangement. In 2019, the Seiryu-kai and Liumang nearly went to war after the Liumang's second-in-command Akira Mabuchi falsified proof that the Seiryu-kai wished to assassinate him and killed two of Captain Mamoru Takabe's officers in retribution, and, with the help of Ichiban Kasuga and his party, Takabe averted a gang war between the organizations and also quelled the internal rebellion within the Seiryu-kai. Chairman Ryuhei Hoshino went on to support Kasuga's campaign for the House of Representatives in opposition to LDP candidate Sota Kume, who was affiliated with the anti-corruption Bleach Japan movement, leading to Governor Ryo Aoki having Jo Sawashiro murder Hoshino. As a result, Takabe rose to become the next Chairman of the Seiryu-kai. After Takabe was imprisoned, clan captain Masataka Ebina became acting chairman, and he outwardly aimed to continue Takabe's goal of securing a "Second Great Dissolution" to disband more yakuza groups. After the Tatara Channel exposed ex-yakuza in their civilian jobs, the Seiryu-kai attracted many ex-yakuza members unable to reintegrate into society, becoming the largest organized crime syndicate in Japan. Ebina then disbanded the clan and transformed it into a revived Bleach Japan in 2023, and he went on to offer several ex-yakuza employment on the radioactive Nele Island, where they would slave away until they died of cancer. Ichiban Kasuga and his friends later exposed the environmentally hazardous nature of the supposedly clean disposal site, putting a stop to Bleach Japan's reformation and leading to Ebina's arrest.