Kei×Yaku: Abunai Aibou

Three years ago, a disappearance known as the Joker Case went unsolved, and the file closed. Renewed interest in the case demands a second examination of the evidence.
Investigator Kinoshita Ichiro from the Public Security Bureau of the Tokyo Metropolitan Police Department is called on for a reunion of the investigation. However, he is assigned a completely different mission. His assignment is to spy on a gang clan led by its young head, Hanabusa Shiro. A man of mystery, Shiro has risen to the rank of Wakagashira (young leading subordinate in the yakuza group) in three short years.
In the course of his mission to get close to Shiro, Ichiro learns a shocking fact, steering him to draw up a fake lover's contract with Shiro. Their undercover operation gradually leads to an incident sure to shake up both the nation and their destinies.
(Source: Blue Poison at MDL; edited by MDL)
~~ Adapted from the manga "Kei×Yaku: Abunai Aibou" (ケイ×ヤク －あぶない相棒－) by Kaoruhara Yoshie (薫原好江).