You Definitely Shouldn't Respond.After Iroha transfers into Kamihama Middle School, she hears from Rena about rumors concerning an "Invisible Girl" and "Endless Solitude", along with one from Tsuruno about an "Electric Wave Girl". The next day, Iroha picks up Felicia after she gets in a fight with people insulting her friends, and two investigate the radio tower, where they hear a laughing voice coming from Iroha's phone. The day afterwards, Iroha notices a connection between the voice and the seemingly spam messages she has been receiving and investigates the radio tower again and encounters Tsukuyo, who brings up someone named Sana Futaba before being chased off by the arrival of Yachiyo and the others...