Rival Otoko (ライバル男; Rival Man) is a duet between Morning Musume members Ono Sayuki and Eguchi Rin. It was released as a B-side for the single Wagamama Kinomama Ai no Joke/Ai no Gundan, August 28, 2013.
- Lyrics: Ono Sayuki & Eguchi Rin
- Arrangement: Ikuta Naoki
- Composition: NICHIDO
- Ono Sayuki & Eguchi Rin
- Rival Otoko: Lyrics
- Member Comments:
- According to Ono Sayuki, they wrote the song in February 2013, and asked Tsunku if they could release it. When Tsunku started making plans for Morning Musume's 54th single, he decided to make the song a B-side.
- According to Eguchi Rin, the song is about two men that fight over a girl, in hopes of winning the girl's heart,but the girl turns them down for another man.