Kayo is Matsu's girlfriend and a sex worker. Matsu, an underling in the Menso yakuza group, faces pressure to abandon his criminal life when Kayo becomes pregnant with his child, their impending family becoming a central catalyst.

After members of the rival Tengenji gang assault Matsu and insult Kayo, Matsu retaliates using a gun entrusted to him by his superior, Sabu. This violent act, provoked by the insult to Kayo, drastically escalates tensions between the gangs, forcing Sabu to intervene to contain the conflict.

Kayo's situation embodies Matsu's internal struggle between his yakuza loyalty and his desire for a stable future with her and their child, though his choices consistently lead to further complications.