Kaname Ohgi emerges as leader of a Japanese resistance cell following Naoto Kozuki's death. Recognizing Zero's superior strategic mind, he steps aside, becoming the Black Knights' Deputy Commander. His compassion drives him to rescue and nurse the injured Britannian officer Villetta Nu, forging a relationship despite her amnesia and potential knowledge of Zero's identity.

During the Black Rebellion, Villetta recovers her memories and shoots Ohgi; he survives. Imprisoned after the uprising's failure, Zero rescues him. Though initially trusting, Ohgi ultimately leads the Black Knights' betrayal of Zero, swayed by Villetta's testimony and Schneizel el Britannia's influence. He sets a trap for Zero using Kallen as bait and agrees to hand him over in exchange for Japan's independence. After Lelouch's ascension as emperor, Ohgi fights in the final battle, faces capture and execution, but is spared by the Zero Requiem.

In the original series conclusion, Ohgi becomes Prime Minister of the United States of Japan and marries Villetta Nu. Within the *Lelouch of the Re;surrection* continuity, he resigns as Prime Minister, burdened by guilt over his betrayal. He runs a cafe with Villetta and their infant son. When Lelouch returns, Ohgi provides intelligence on Zilkhstan and joins the mission to rescue Nunnally vi Britannia. Overwhelmed by remorse, Ohgi attempts suicide to atone, only for Lelouch to intervene and forgive him.

Ohgi subsequently aids the Zilkhstan infiltration, following Lelouch's commands. After the mission succeeds, he reflects on their actions with Tamaki before returning to his family life.