Yūgo Kakitani fights against AI as a member of Toak. His opposition originates from a childhood trauma: witnessing his piano teacher AI shatter while saving humans during an accident. This violation of the single-mission principle fostered his deep-seated resentment.

He engages in Toak operations, including a raid targeting politician Yōichi Aikawa. Critically injured during this mission, his survival hinges on Vivy's repeated interventions, establishing a complex dynamic between them despite his unwavering stance against AI.

Severely wounded, Kakitani undergoes extensive bio-integration with android components to prolong his life. This technological dependence sustains him for decades, creating a personal contradiction. Roughly 40 years after first encountering Vivy, he forms an agreement with Ophelia's advisor AI, Antonio, further complicating his relationship with artificial beings.

Before dying, Kakitani installs malware onto the songstress AI Diva. This malware erases Diva's core persona, directly impairing Vivy's singing ability and creating lasting consequences.

He has a granddaughter, Yui Kakitani, who uses a wheelchair, confirming his continuation of a human family line despite his prolonged, technologically augmented existence.