Homeland: Planet Kinniku, Age: 14 (Choujin Olympics: 15, Ultimate Tag: 16), Height: 176cm/5'9", Weight: 83kg/189lbs., Chojin Power: 930,000. The main character of the story. He is the 59th prince of Planet Muscle (Planet Kinniku) and son the first Kinnikuman, Suguru Muscle and Belinda/Bibinba. Raised during times of peace, he is a spoiled, cowardly, lazy teenager, much like his father was at the beginning of the first series except with more emphasis on cowardice and less on clumsiness. He usually start matches off in a cowardly state, only managing to get a few good moves in due to luck. However, when his friends are in trouble or his opponent is being dishonorable, he manages to reach the state of Kajiba no Kuso Djikara (Burning Inner Strength). When this happens, the Niku-Mark appears on his forehead and his strength, stamina, and technique increase many fold. Because Suguru had his records annulled years ago, Mantaro never knew how great a hero his father really was until he met Alexandria Meat. Mantaro was named after Ultraman Taro (Ultraman + Taro/Kinniku + Mantaro). Mantaro's favorite wrestling move is his father's signature move, the Kinniku Buster (sometimes called the Butt Buster in the English dub, though it actually translates to Muscle Buster) which he won much of his wrestling matches with until he gains his own signature move, Muscle Millennium. Mantaro is rather lecherous and lusts after many girls, but his main love interest is Rinko Nikaido (Roxanne). His favorite food is galbi bowl (Beef and Rice), which he often sings about.
In the Japanese version of the anime, Mantaro has a habit of adding Muscle (マッスル Massuru) at the end of certain words and sentences in place of the standard masu (ます). For example, Itadaki-masu (いただきます), a common Japanese phrase said before eating, becomes Itadaki-MUSCLE (いただきマッスル Itadaki Massuru).

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