First appearance: Battle 70
Age: 20
Height: 195cm
Weight: 200kg
Type: Dou
Type: Katsujin Ken
Martial Arts: Combat Sumo

Chiaki Yumai, or Thor, as he is more commonly known, was formerly the Seventh Fist of Ragnarok and currently a captain for the Shinpaku Alliance. Thor is a very tall and well-built young man with a fat, yet very muscled physique and has short black hair and dark sideburns that stick out. He typically is seen wearing a sleeveless kimono to show off his muscular arms and usually doesn't wear any footwear.

He fights using a combat-sumo fighting style and joined Ragnarok in order to make his dream of making the combat-sumo style mainstream. Despite being in Ragnarok, Thor has a high degree of honor, capable of reasoning with foes, and considers upholding the rules of combat-sumo wrestling his top priority. Thor is also perceptive, even while in an imminent rage, having immediately discerned exactly who Kenichi was after their first encounter based on the information that Siegfried passed on to him. Thor believes that the Shinpaku Alliance is composed of true comrades, unlike Ragnarok, during which he believed Siegfried was the only person who was his comrade.

Thor has a strong liking for fellow Sumo Wrestlers. Such as in the D of D Tournament, he cheered for one. He also says things that most Sumo Wrestlers say. Thor is also afraid of heights, such as when he needed to jump out of a helicopter, he grabbed the side stating he couldn't do it. However, he put his fear behind him for the sake of his friends.

Thor practices a hybrid martial art heavily based on traditional sumo. An interesting note about Thor is that he was never trained by any master in combat-sumo, yet he achieved his level by pure hard work and training. Takeda Ikki even said that Thor, who achieved his level without a master is "simply beyond belief", demonstrating that underneath his supposed stupidity, he shows ability through his determination and hard work as a martial artist. Thor would later receive some training from Kugatachi Danki, greatly boosting his already formidable fighting skills.