Somei visits her neighbor, Katori, a few months before First Large-Scale Invasion, where she's greeted by the latter's family. During the invasion, both of their houses were destroyed and they were hospitalized when the invasion occurs. When Border's HQ was completed, Somei states her desire to join.
Note:The chapter is narrated as a flashback.
Somei visits Katori's house to play, where Katori is playing video games. Katori's mother acknowledges that Somei is the hard worker while Katori slacks off. Katori retorts by saying that her marks are fairly high despite not studying. Somei simply responds that Katori is benefitting from the situation, therefore she cannot change when Katori's mother asks how Katori can change. Somei's father then arrives, telling Katori's family that Somei will no longer visit because she was unable to be top of the class. Later, Katori changes rooms with her brother to be beside Somei's room. Katori asks Somei why she only studies. Somei responds that the world changes so often, it's best to keep up with it.
During the First Large-Scale Invasion, Katori's house is demolished. Katori is under debris, but is rescued by Somei. Somei takes Katori to the hospital, despite Katori's family seemingly being still under the house. At the hospital, Katori's family is reunited with Katori; however, Somei's family was killed. When asked by Katori why she didn't choose her family, all Somei says is that it had a higher probability of success. Following the invasion, Somei decides to remain in Mikado City and decides to join Border. Katori decides to join too, believing her genius combined with Somei's abilities can make them rise to number one easily.
While in the present, Katori is enraged by Osamu's desire to help people.