Jyunichi is the silent second-in-command and chief enforcer of the Ronin. He is a tall young man with a muscular body. His head is always shaven and he has numerous Japanese-style tattoos on several parts of his body. He is very skilled in sword fighting, to the extent that he can effectively wield dual katana and never uses a gun. He also has a great sense of honor, and practices strict temperance against hedonism. Jyunichi is very loyal and respectful to almost all Ronin members who possess a higher ranking than him. The only exception would be Shogo Akuji, who aside from being an ineffective leader, lacks the honor, valor, and discipline Jyunichi expects one in Shogo's position to have.
After the Saints robbed the Poseidon's Palace, Shogo sent Jyunichi to scout the Saints for any possible weakness. He found one in Aisha, the lover and girlfriend of Johnny Gat, the Saints' second-in-command. While the Boss and Johnny were busy elsewhere, Jyunichi broke into Aisha's house and set up a trap, tying Aisha to a chair and telling her he would let her live if she cooperated. However, as the Boss and Johnny entered the house, Aisha shouted a warning, prompting Jyunichi to instantly decapitate her. Johnny barged in to find his lover dead, his house filled with Ronin, and his lover's murderer before him. Johnny kills one of the Ronin close to the door and manages to take his katana, Jyunichi unsheathing one of his own and beginning to fight Gat while the Boss killed Jyunichi's underlings. One Ronin aimed his gun towards Johnny, only to have it knocked out of his hand by a well-thrown katana by Jyunichi, as he declared, "He's mine!" in Japanese. The Boss told Johnny to move so he could get a clear shot at Jyunichi, Gat turns as the Boss speaks, losing his footing and Jyunichi quickly stabs him in the stomach. With the Boss unable to help due to his gun being empty, Jyunichi retreats as the Boss reloads.
While going to the airport to pick up Kazuo Akuji, Jyunichi spotted the Boss and Saints' strategist Pierce Washington making their way to Akuji's plane, Jyunichi thus broke through the airport security and warned Akuji ahead of time. Akuji's entourage stayed behind to help guard their leader's escape. When Shogo called to ask for his father, Jyunichi berates him, saying that he should have been the one to protect his father, and should have been there when his father landed.
Shogo, angered by Jyunichi's words, anonymously calls the Boss, and gives him the location of Jyunichi, Kanto, Jyunichi then challenged the Boss to a sword duel, his own Ronin helping him. Jyunichi fought the Boss to the death.