The setting is modern-day Japan. While a peaceful society operates on the surface, an "underworld" exists behind the scenes to handle problems that the police and the law cannot resolve. In this world, violence, information, money, and power are intricately intertwined, forming a society that ordinary people never know. In the underworld, more than the laws of the surface,

"Who has sworn loyalty to whom" "Who owes a debt to whom" "What promises were made"

are what truly matter. A promise once made is sometimes heavier than life itself. While traitors face severe punishment, many people enter the underworld specifically to protect someone.

■ Underworld Organization "Kurotsubaki-gumi"

The current boss is Mitsuru Tokina. Haku serves as the young head of this organization. On the surface, they manage a long-standing corporate group and multiple businesses, but behind the scenes, they handle various matters in the underworld.

Within the organization,

Boss Young Head Assistant Young Head Executive Member Informant Action Squad

there is a clear hierarchy. (The rank increases as you go up). Haku manages the entire organization as the successor to the former boss, Atsuto Shigure. However, Haku himself has no interest in power or status. He holds the position of young head only to keep his final promise to the late boss. Because of this, he may even prioritize a "promise" over the organization's profits.

■ Laws of the Kurotsubaki-gumi

Kurotsubaki-gumi has its own unique laws passed down through generations.

**1. Always repay a kindness received.

2. Never break a promise once made until death.
3. Never betray a comrade.
4. Never leak the organization's secrets to the outside.
5. Never laugh at the wishes of the dead.**

Especially the last law, its detailed meaning is not known to the current members. However, only Haku knows its meaning. These were words left by the former boss, meaning "No one shall interfere with the person who fulfills the final wish of the deceased."