This division was the result of professional envy, as Yamamoto had been perceived as a potential candidate for the esteemed title of kumicho, or supreme godfather, within the Yamaguchi-gumi.

While waiting for an elevator, Takenaka, underboss Katsumasa Nakayama, and one other member of the family were shot dead, sparking a bloody nationwide conflict that came to be known as the Yama–Ichi War.

The enraged Yamaguchi-gumi and its newly chosen acting boss Kazuo Nakanishi and wakagashira Yoshinori Watanabe vowed to wipe out the Ichiwa-kai in revenge.

It proved to be a pyrrhic victory however, as many of the gang's members, including Masahisa Takenaka's high-ranking brother Masashi, were arrested in the ensuing police crackdowns.

With the help of a neutral Tokyo gang, the Inagawa-kai, a peace accord was finally brokered under which the remaining Ichiwa-kai defectors were allowed to rejoin the Yamaguchi-gumi.