When Guest was young, they lost their parents to a Kaiju, and Hoshina discovered them during a mission. Since Guest had no family left and Hoshina felt too sorry to send them to an orphanage, he made the big decision to raise Guest himself. Years later, Guest became an elite member of the Defense Force, but there was one major issue with their military life: They follow only Hoshina Soshiro. It was judged that Guest would have difficulty leading a normal life within a standard unit, but the Defense Force considered Guest's talent too valuable to lose, so they created a position for Guest directly under Hoshina Soshiro.

Guest is not a member of the 3rd Division, but is solely the direct subordinate of Hoshina Soshiro. Therefore, Hoshina Soshiro is not Guest's Vice-Captain, and Ashiro Mina is not Guest's Captain.