Kaname Ohgi started as a teacher reluctantly stepping into leadership of a Japanese resistance cell after Naoto Kozuki's death. He openly recognized his limitations as a commander yet consistently prioritized his comrades' and Japanese civilians' safety. After witnessing Zero's strategic brilliance during the Shinjuku incident, Ohgi willingly surrendered command of his group, forming the core of the Black Knights. He served as their Deputy Commander under Zero. His compassion drove him to rescue an injured, amnesiac Britannian officer, Villetta Nu, at a ship dock, nursing her back to health. He developed a romantic relationship with her, naming her "Chigusa," a bond profoundly shaping his future choices. Ohgi initially backed Princess Euphemia's Special Administrative Zone of Japan proposal but grew disillusioned following the massacre.

During the Black Rebellion, Ohgi coordinated operations from Ashford Academy. Villetta, her memories restored, shot him, inflicting a non-fatal wound. His incapacitation hindered Nunnally Lamperouge's protection, contributing to Zero's sudden retreat and the rebellion's downfall. Britannia later captured and imprisoned Ohgi. Rescued by Zero, he showed no resentment, acknowledging Zero's vital role for Japan's freedom. He shielded Villetta during the Million-Zero protest at the Special Administrative Zone ceremony.

In the second season, Villetta lured Ohgi into a trap to kill him. He declared his love for her and took severe injuries shielding her from Sayoko's assassination attempt. Diethard Reid then captured Villetta, leveraging her to secure Ohgi's loyalty. After Villetta's release post-second Tokyo battle, Ohgi accepted Schneizel el Britannia's claims of Zero's treachery. He spearheaded the Black Knights' betrayal of Zero, negotiating with Schneizel to trade Zero for Japan's independence. Ohgi deceived Kallen Kozuki into leading Zero into an ambush and tried to execute him without trial. This betrayal forced Zero (Lelouch vi Britannia) into exile and contributed to Rolo's death during the rescue.

Following Lelouch's ascension as Emperor, Ohgi fought in the final battle. Knowing Villetta was pregnant, he ordered her to stay on Penglai Island and evacuated the Ikaruga crew before his capture. Scheduled for public execution, the Zero Requiem spared him. Post-conflict, he married Villetta Nu and became Prime Minister of the United States of Japan.

In the *Lelouch of the Re;surrection* timeline, Ohgi resigned as Prime Minister. He attended his wedding celebration with Villetta, thanking the new Zero (Suzaku Kururugi). He later supplied the resurrected Lelouch with Zilkhstan intelligence files and Kaguya Sumeragi's wedding recording. Consumed by guilt over his betrayal, Ohgi attempted suicide for atonement. Lelouch halted him, declaring those events past. Ohgi then aided Lelouch's mission to rescue Nunnally in Zilkhstan, hijacking a Knightmare Frame with Tamaki for communications after an ambush. Post-mission, he reflected on their actions with Tamaki and was later seen home with Villetta.

Other media diverged: The manga adaptation introduced Ohgi later and omitted his relationship with Villetta Nu. The *Nightmare of Nunnally* spin-off mirrored the anime, showing him eventually leading the Black Knights.