Kazuki is the proprietor of the Stardust bar, and the boss of Yuya, who is the club's manager. He is one of Kiryu's allies.
After the clash between Yuya and Kiryu, Kazuki apologizes Kiryu for not letting Yuya know Kiryu have an appointment with him. Then, Shimano's boy go to Stardust and want Kazuki give them protection money, Yuya argues Shimano's boy to kicking them out from Stardust. Yuya won't let Kazuki pay Shimano's men, Kiryu helps out fighting them off.
Yakuza 2 Edit
He was kidnapped 6 months before the game started, so in Stardust is the fake Kazuki. After being shot by the fake Kazuki and rescued by Kawara, Date, Kiryu and Kaoru Sayama, he is at Emoto Clinic until the end of the game.
Yakuza 3 Edit
He is still at Emoto Clinic at the beginning. In the end, he and Yuya catch Hamazaki, who stabs Kiryu Kazuma before.
Yakuza 4 Edit
Kazuki has become almost a minor character with little to no involvement to the game main story.
Post-Yakuza 4 Edit
In Yakuza 5, Yuya mentioned that Kazuki still runs the club. However, when the events of Yakuza 6 take place, Yuya mentioned that the club is bought by the Jingweon mafia and that Kazuki wanted to repurchase the business.
Compared to Yuya, Kazuki has a much more composed manner. Being put under Shintaro Kazama's wings, he's also a skilled businessman, able to raise Stardust to a point where it becomes Kamurocho's top host club without having to rely on protection.