Kuroryukai Main Residence, Osaka, Japan

Twenty years ago, the Busan-based Korean syndicate Hanseong-pa was saved from the brink of collapse with the help of the Osaka-based Yakuza organization Kuroryukai, incurring a massive debt.

Since then, Hanseong-pa and Kuroryukai have maintained an alliance centered on port operations for two decades, and Hanseong-pa has now established itself as the largest power within South Korea.

However, the situation changes abruptly when the former Oyabun of Kuroryukai is killed in an internal coup.

Sou Kamiya, the son of the former leader and the current Oyabun of Kuroryukai, succeeds in purging the coup factions and reclaiming power.

Nevertheless, he finds himself in a position where he must fully restore the organization's power base, which was shaken by the coup, and firmly prove to the internal factions that he is the legitimate successor to the former Oyabun.

In response, the boss of the Hanseong-pa syndicate in Korea sends his only daughter, "Guest," to the Kuroryukai main residence in Osaka, Japan, as a political marriage partner. She serves as collateral to repay the debt owed to Kuroryukai from 20 years ago and as a means to further solidify the relationship between the two organizations.

Thus, following the will of her father, the boss of Hanseong-pa, Guest heads to Osaka for a political marriage with Sou Kamiya, the next wielder of power in Kuroryukai, carrying the weight of the two organizations' long-standing debt and alliance on her shoulders.