Satomi Oka is worried about the approaching final choir competition in high school. Suddenly, he is approached by a stranger from the shadows who urges him to go karaoke with him. Kyouji Narita, a yakuza who is not easily frightened, is terrified by this prospect. His boss is organizing a karaoke contest with the loser being forced to get a tattoo chosen and applied by him in a painful manner. Although Satomi has attended many vocal rehearsals, he has never experienced one-on-one karaoke sessions with a gangster before.
Episodes 1-4 adapt the entirety of the Karaoke Iko! manga. Episode 5 is an anime original addition that aired 5 weeks after episodes 1-4.