Yoko Yabuki is a police officer and the romantic partner of protagonist Goku Furinji, serving as his professional partner. During their investigation into a criminal organization that killed fellow officers, she suffers a critical injury when the group's leader deploys specialized bees programmed to target human breath. This attack leaves her fatally wounded or comatose, becoming the primary catalyst for Goku's vengeful pursuit of the organization and its leader.

Physically, Yoko has black hair and frequently wears a red tracksuit. Her role in the narrative focuses on escalating the protagonist's personal stakes and emotional drive following her injury.