Yukio Tonegawa (利根川 幸雄) is who was put in charge of most of Hyōdō's events, acting as said mans right hand. He is a powerful business magnate and the third highest ranking executive in the financial firm Teiai Corporation.
He serves as the second main antagonist in the Tobaku Mokushiroku Kaiji arc.
He has a spinoff manga called Chuukan Kanriroku Tonegawa where he is the main protagonist.
A stout man of middle-age, Tonegawa is a staunch realist, believing those who risk their lives in Love Emperor's tournaments to be street trash at the mercy of society and those with superior abilities and initiative. By reputation Tonegawa is a master of human psychology and the art of observation, displaying acts of insight so profound his abilities appear supernatural.
Chuukan Kanriroku Tonegawa
In the spinoff manga he appears to be less calm and more stressed and emotional compared to his depiction in the main series due to Hyōdō's more comedic antics and abuse towards him.
In the anime adaptation he manages to maintain his stern demeanor as depicted in the main anime series.
Tobaku Mokushiroku Kaiji
He is first introduced in the series as the sponsor on the Espoir and explains the rules behind Restricted Rock, Paper, Scissors.
After the Human Derby, he is again the sponsor behind the Electric Current Steel Frame Crossing and explains to the participants how they can obtain the prize money they were promised in finishing the Human Derby. He then sits down and gives commentary about the situation the participants face when they are crossing the steel beams.
After Kaiji manages to finish the Steel Crossing, he later serves as his opponent at the Starside Hotel in E-Card. Here, Kaiji is forced to bet an ear or eye to compensate for the amount of money being bet which he lacked.
In the gamble Kaiji manages to outwit him by realizing how he manages to monitor his emotions. He is defeated by Kaiji and is ordered by Hyōdō to apologize to him for all the misfortune he had caused Kaiji and his companions earlier.
Then, Hyōdō replied that no matter how much a person has begged for forgiveness they would never truly mean it and then ordered his men to bring out a massive smoldering frying pan where he ordered Tonegawa to kneel on it to Kaiji out of his sadistic pleasure. Tonegawa, showing how dedicated he was to his superior, manages to kneel on it based on his own will alone. Now heavily burned and unconscious, he is dragged away by his men in defeat.
Tonegawas fate is left unknown. However it is certain that he was demoted from second-in-command in the Teiai Corporation.
Tobaku Hakairoku Kaiji
During the Bog arc, it was revealed that Tonegawa had won at the machine 1 year prior to Kaiji's arrival at the underground casino, and that Hyodo had won a couple of years before him. Kaiji seemed shock at this reveal.