Raised on the streets of Utsunomiya, Tochigi Prefecture, young street urchin Leiko Tanaka fell in with the Shikei-otaku, one of the many youth-based motorcycle gangs (bōsōzoku) involved in Yakuza activities. At age 18, she was arrested during a botched robbery of the Kiyohara Industrial Complex and sentenced to a term of five years in Tochigi Prison. However, before serving her full sentence, engineers from Japan's Ministry of Defense came to her with a deal: secure an early release from prison in exchange for test piloting an experimental exosuit. Tanaka, who was chosen as a test subject based on her good behavior in prison and her high-speed motorcycling skills, accepted the government's terms and soon found herself in the "Go-Go Tomago" exosuit, named for the sphere-like shape the armor takes when propelling through the air at high velocities ("tomago" being a corruption of "tamago", the Japanese word for "egg").
When the top-secret consortium of Japanese politicians and business entities known as the Giri was formed to recruit and train potential superhuman operatives for Big Hero 6, Go-Go Tomago was chosen to be a founding member of the team due to her proficiency with the exosuit and the belief that her fear of being sent back to prison would make it easy for the Giri to control her. Impulsive and hotheaded, Go-Go initially clashed with virtually every member of her new team. She refused to take orders from the team's initial field leader, Silver Samurai (Kenuichio Harada), and was insanely jealous of teammate Honey Lemon (Aiko Miyazaki). However, once becoming acclimated to the team, her grudging respect for her teammates evolved into true kinship