Ijuin is a minor antagonist featured in Yakuza 4.
In 2010, when Ueno Seiwa Clan captain Isao Katsuragi agrees to meet with Kazuma Kiryu atop Kamurocho Hills to negotiate for the release of his captives, the siblings Taiga and Yasuko Saejima, he decides to reduce the chances that Kiryu will beat him up when he arrives to the meeting. In order to do so, he orders all the men of the Ueno Seiwa Clan that he has available at the time to go to Kamurocho Hills and attack Kiryu as he makes his way up, in order to tire him as much as possible before the confrontation.
Ijuin is the fourth of the Ueno Seiwa lieutenants that Kiryu encounters as he fights his way up the building. He is encountered in the penultimate floor of the construction site, where he awaits as the final obstacle between Kiryu and Katsuragi. When Kiryu confronts him, they are joined by Horie, Nakanowatari and Suzumiya; the three other Ueno lieutenants Kiryu defeated on the way up.
The four lieutenants join forces to fight Kiryu together but, in spite of their combined might, the Tojo chairman is still able to defeat them all and proceeds to the last floor to confront Katsuragi.
Ijuin appears to be trained in taekwondo, with his attacks mostly consisting of various forms of kicks as well as some acrobatic flips.
He is the most aggressive of the four lieutenants and will pursue Kiryu throughout the arena where he is fought. If Kiryu retreats, he will attack with a running roundhouse kick which can stun Kiryu and leave him open for a deadly combo from behind. If locked into a combo himself, Ijuin will try to interrupt it with a backflip that knocks Kiryu back.