The main antagonist of Muscle Returns.
A very powerful Chōjin who bursts onto the scene and easily takes out Warsman, Terryman, and Buffaloman. He is the master of Great Taijutsu, a martial art brought to Brazil from Japan 130 years prior. He is eventually defeated by Kinnikuman. Buki Boy is known to defeat all his opponents within a five-minute time-frame.
During the first Chojin Ultimate Championship, Buki Boy is introduced as a newcomer that has just defeated Warsman.  This is followed by a semi-finals fight against Buffaloman; after knocking Buffaloman unconscious, Harabote Muscle - as referee - declares the match has ended. Buki Boy continues to attack, refusing to believe that Buffaloman has been defeated. Geronimo and Terryman fight him back, after it is revealed Buffaloman's neck has been broken. 
The bell is rung for the final match, which shall be between Terryman and Buki Boy. Geronimo acts as Terryman's second, but Buki Boy starts the match with his Dazzling Eyes. Terryman tries to attack, but Buki Boy counters with a Back Throw, and takes him in a Rear Choke Hold, which Terryman dodges and counters - in turn - with a Texas Clover Hold. Buki Boy headbutts him to escape, and proceeds to dislocate all of his limbs in order to tie Terryman together into a knot. He wins with a Weapon Lightning Drop. Buki Boy takes the championship belt. The crowd cheers for Buki Boy. 
Buki Boy demands any Seigi Chojin challenge him within three days. Robin Mask - as the sole surviving chojin - is determined to be the one to defeat him, despite his injuries that could result in death. At the match itself, held at the Tokyo Dome, Robin Mask is heavily outmatched by Buki Boy, until Kinnikuman arrives and stops him in his destruction of Robin Mask. Ramenman warns Kinnikuman not to charge, and Geronimo warns him not to look in Buki Boy's eyes, and this allows Kinnikuman to get to a good start. Buki Boy attempts a German Suplex, but Kinnikuman counters with an Ass Cheeks Scissor. Buki Boy attempts a Tombstone Pile Driver, but Kinnikuman stops him with a fart. He follows this up with a Trunks Driver. 
Although Buki Boy is unable to read his attacks, he eventually gains the upper hand and sets up for his Weapon Lightning Drop (which defeated Terryman). The cheering of the crowds inspires him to break free, before he counters with a Kinniku Buster. This defeats Buki Boy, who is not seen again in the manga. 
Weapon Lightning Drop (武器・雷槌落とし Buki Ikazuchi Otoshi)
- Dislocates his opponent's limbs, ties them into a knot, and slams them into the mat
Dazzling Eyes (幻惑瞼 Genwaku Manabuta)
- He causes his opponent's body to move on its own
Win/Loss Record (Singles)
- O Warsman (Rear Choke Hold)
- O Buffaloman (Read Choke Hold) (1 minute 28 seconds)
- O Terryman (Weapon Lightning Drop)
- X Kinnikuman
- Fighting Style: Great Taijutsu (グレート躰術)
- Since Muscle Returns is a non-canon chapter. It can be assume that Buki Boy is non-existed in the main timeline.