He is the main antagonist in the Tobaku Datenroku Kaiji arc.
Muraoka is a pop-eyed, middle aged man with dark, loose, wavy, shoulder-length hair. His facial features consist of a long, trapezoidal face and a nose in the shape of a downward cross.
In the pachinko animation, he has slightly darker skin than other characters, presumably due to tan.
In the manga he is seen wearing a light brown lounge suit with a red shirt underneath, a long yellowish tie and dress shoes.
He is employed as a casino president at one of the casinos under the management of the Teiai Corporation. At some point, he employs Miyoshi and Maeda after the events of the Bog and has heard of the amount of money Kaiji managed to win from it. He assumed that Kaiji won all the money for himself and was keeping it hidden away.
Tobaku Datenroku Kaiji
He has Miyoshi and Maeda secretly convince Kaiji to gamble against him in Mine Field Game “17 Steps”, which he has rigged in his favor by having Maeda look at Kaiji's tiles while Miyoshi gives Kaiji false information. Initially, Kaiji was made to believe that they were working on his side only to realize while playing and losing enough money that the flow of the game felt off as they were constantly feeding him wrong information and making mistakes.
Although Kaiji initially loses all his money, Kazuya Hyōdō loans him more money so the game can continue. After several draws where the wager is doubled and it reaches ¥160 million.
By tricking the casino president into thinking he had another tile, Kaiji is able to win ¥480 million due to him having ura-dora. Due to his massive lose, Muraoka manages to piss in his pants due to his tremendous loss.
Tobaku Datenroku Kaiji: One Poker-hen
He is seen at the beginning of the arc talking to Miyoshi and Maeda about losing all his money and attempting to force them to pay him back, with the latter saying it is impossible for them to back such a large amount. He then claims he will kill himself if left alone.