Kiryu is the main protagonist in the Yakuza (Ryu ga gotoku) series. Born on November 6, 1968, he was raised during the 1970s in the Sunflower Orphanage with Akira "Nishiki" Nishikiyama, who became his best friend, the latter's sister Yuko and Yumi Sawamura who joined in 1980. When he was a child his parents were killed by Shintaro Kazama, a Tojo Clan affiliate Dojima Family lieutenant, who brought him to the Sunflower orphanage he financed. Later Kazama introduced Kiryu and Nishikiyama in the Dojima Family. Kazama became a father figure for Kiryu who supported him within the Family and years later when he was released from prison. Kiryu rose through the Tojo hierarchy and earned the nickname "the Dragon of Dojima" (堂島の龍, Dōjima no Ryū) because of the dragon tattoo on his back. He was planning on starting his own subsidiary group until he took the blame for the murder of his boss, Sohei Dojima, to protect his best friend, Nishikiyama, and was imprisoned for ten years.

37 years old. 184 cm, 88 kg. December 2005, after his release, Kiryu returns to his home town, Kamurocho, but due to his patricide he is marked for death by the entire yakuza community. He quickly finds himself pulled back into the Yakuza underworld. He befriends Kazuki and Yuya, the owner and manager of Stardust, a host club. Kiryu then learns that 10 billion yen has been stolen from the Tojo Clan. Soon after he meets a young girl called Haruka, whom seemingly every criminal group in the country is after. Upon reuniting with Yumi, his childhood love and Haruka's mother he is confronted by Kyohei Jingu, Haruka's father, and the true owner of the money. Yumi, intending to destroy the money so no one can have it, has set a bomb in the bar. After defeating Jingu, Kiryu is reunited with his old friend Nishikiyama. The two fight, with Kiryu coming out victorious. Jingu tries to shoot Kiryu but Yumi takes the bullet for him. Nishikiyama then stabs Jingu and intentionally setting off the bomb. The money falls from the sky, and Yumi dies in Kiryu's arms. Kiryu subsequently decides to start a new, honest life with Haruka.

When the fifth Chairman of the Tojo Clan, Yukio Terada, is assassinated on December 15, 2006, Kazuma Kiryu wants Sohei Dojima's son Daigo to take the clan's leadership and prevent an upcoming yakuza families war, but the young man doesn't want the responsibility. While attempting to broker a peace deal between the Tojo and the Omi, Daigo and Jin Goda, Omi chairman, are kidnapped by Ryuji Goda, Jin's adopted son. Ryuji, through working with the Jingweon mafia, attempts to destroy Kamurocho and Kiryu to be the only dragon in Japan. Kiryu is put under the protective custody of a female detective called Kaoru Sayama, who uses him to get close to the Tojo to discover her past. Eventually, Kiryu and Ryuji fight atop Kamurocho Hills. Kiryu is victorious, buy Yukio Terada appears, revealing that he faked his own death to start a war and is really a Jingweon survivor. Terada is also defeated, but begs Kiryu to trust him. After Jin Goda, Takashima and Terada are dead, Kiryu and Ryuji have a final showdown, which Kiryu wins. A bomb Terada had triggered, but secretly removed the fuse from, fails to detonate, saving Kiryu and Kaoru's lives.

Kazuma Kiryu leaves Kamurocho for Okinawa, where he now runs the Sunshine Orphanage. There he raises nine children, including Haruka Sawamura. He is caught up in a government plot when Sunshine's land is in the way of a proposed resort.

Now 41 years old, Kiryu continues to run the orphanage. However, he is once again involved in the matters back in Kamurocho, having found Saejima washed ashore one day. Saejima tells him a man called Hamazaki told him to find Kiryu, shocking him and Haruka. Some time after Saejima leaves, Hamazaki washes ashore. After meeting up with Yasuko, Hamazaki sends the two on ahead to Kamurocho. There Kiryu leaves Yasuko at New Serena, but returns to find her missing after witness Majima being arrested and dragged away from Millenium Tower to police patrol cars. He chases her into the sewers, where Tanimura and Akiyama mistake him for an Ueno Seiwa Clan member, and attack. After defeating them Kiryu chases Yasuko to the roof, where he finds her and Saejima bound and gagged by Katsuragi. During the events that follow Yasuko is shot and kills Katsuragi before dying herself. Kiryu later fights Daigo on top of the Millennium Tower.

During the events of the zombie spinoff Ryū ga Gotoku Of the End, he returns to Kamurocho after Haruka is kidnapped by a mysterious man. Once there, he discovers the town in ruins and infested with zombies