Yuuki Anzai (安斎 結貴, Anzai Yūki) is the male protagonist of the Devils' Line series. He is a half-devil, half-human hybrid and a police officer who is initially a member of the F Squad in the MPD Public Safety Division 5, responsible to combat devil crimes as well as arresting devils. His occupation as a police officer utilizes his abilities as a hybrid. He is a part of the 15th Hybrid Birth Project at ONLO in Hokkaido, where he was born and raised. Although he isn't a pure-blooded devil, he still yearns for blood like any other devil but has a strict rule of not drinking blood. He has always despised the devil inside of him and devils in general, which is why he also was pessimistic regarding the co-existence of devils and humans. However, his thinking has been changing since he met Tsukasa Taira, who became his girlfriend throughout the series. Following the F Squad's disbandment, Yuuki became a member of the East Bay Public Security Section 1, Squad 3, going under the alias "Alpha Two".