Ikuo Ryuzaki witnessed murder of his sensei 15 years prior to the beginning of manga. As the incident was covered up, he swore, along with his childhood friend, Tatsuya, to find the culprit behind his sensei's death and bring him to justice.

Nowdays, 15 years after the incident and sensei's death, Ikuo Ryuzaki is an sergeant in 2nd Division of Police department.