幼馴染の修平もマンションに取り残されていることを聞き、電話をかける涼花。
合流する修平を待つ涼花に母が話した「X（サイ）」 の生態とは……
Suzuka hears that her childhood friend Shuuhei has also been left behind in the apartment, so she calls him.
As she waits for Shuuhei to join them, Suzuka's mother tells her about the biology of "X (Sai)"...
