Kazuma Sohma became Kyo Sohma's adoptive father after Kyo's mother died and his biological father rejected him. This act was driven by Kazuma's guilt over his own childhood rejection of his grandfather, the previous Cat spirit. Kazuma had once refused candy offered by his grandfather during their only meeting, calling it "cursed," though his grandfather forgave him. Learning that his grandmother stayed with his grandfather out of pity deeply affected Kazuma, motivating his decision to raise Kyo as atonement.

He runs a martial arts dojo near the Sohma main house, training younger Sohmas including Kyo, Kagura, Yuki, and Hatsuharu. Due to practical shortcomings like notable clumsiness and a lack of basic life skills—particularly cooking, which he remains unaware of—his daily life is managed by his assistant, Kunimitsu Tomoda. Despite these quirks, Kazuma maintains a disciplined and traditional lifestyle, typically wearing a dark blue kimono.

Personality-wise, Kazuma is wise, level-headed, and compassionate, though he harbors self-critical views, considering himself selfish for imposing his feelings on Kyo. He initially kept emotional distance, fearing his paternal affection might burden Kyo, especially after Kyo repeatedly denied seeing him as a father. Kazuma fearlessly defies Sohma family norms to protect Kyo, including openly opposing Akito Sohma to secure Kyo's future happiness. His guidance emphasizes resilience, reminding Kyo that "despair will attack you again and again... hope will return to you again and again."

A pivotal moment occurs when Kazuma deliberately removes Kyo's rosary, exposing his true monstrous form to Tohru Honda. This tests Tohru's sincerity, as Kazuma feared her kindness might stem from pity like his grandmother's. After Tohru accepts Kyo in this state, Kazuma reconciles fully with Kyo, who vows to become worthy of calling him "father." Kazuma then cuts his hair—previously grown long as a superstitious gesture for Kyo's protection—symbolizing a new beginning.

Beyond Kyo, Kazuma provides sanctuary for other Sohmas, such as Isuzu Sohma (Rin), allowing her to recover at his dojo after incidents involving Akito. In the series' conclusion, Saki Hanajima works as a cook at his dojo, with implications of a closer relationship, though an author note clarifies Kazuma views her primarily as Kyo's classmate. Kazuma remains a stabilizing figure for the Sohma family, embodying quiet strength and selfless dedication.