Mogura no Uta

Reiji Kikukawa is a young, hot-headed police officer who plays by his own set of rules. When his personal views on how to do his job, no one is shocked when he is finally fired. However, in reality, he is secretly tasked with going undercover to infiltrate a dangerous yakuza group, the Sukiya organization and find evidence to arrest its leader, Shuho Todoroki.