- Name: Mari Nikaidō (二階堂マリ, Nikaidō Mari)
- Classification: Earthling
- Homeland: Japan
- First Appearance: Manga Chapter 6, Anime Episode 3, Kinnikuman II: Anime Episode 17
- Seiyu: Chisato Nakajima; Miki Inoue (Kinnikuman: Scramble for the Throne and Kinnikuman Nisei)
- Mari Nikaido is a Yamato nadeshiko-type that was Kinnikuman's original love interest in the series for the first three story arcs. The anime on the other hand, kept her as the love interest for the entire series throughout the 80s and 90s.
Mari is a daycare worker at Suminoe Kindergarten that inexplicably falls for Kinnikuman.
When Bibimbap arrives, she feels overshadowed by her and gives up on Kinnikuman, going overseas to study.
- Theme Song
- "Catch Me, My Hero" by Kaori Kumiko.
- Suminoe Preschool Daycare Worker (Principal in Nisei)