You Definitely Shouldn't Respond is the title of the eighth episode of the Magia Record: Puella Magi Madoka Magica Side Story anime.
Iroha transfers into Kamihama Middle School and hears rumors from Rena concerning an "Invisible Girl" and "Endless Solitude". There is a further rumor on an "Electric Wave Girl" heard from Tsuruno.
Felicia is picked up by Iroha after she fought with people who had insulted her friends. As they investigate the radio tower, they hear a voice laughing from Iroha's phone.
Noticing a connection between the laughing voice and messages, Iroha returns to the radio tower to find Tsukuyo. Sana Futaba is mentioned before they leave in response to Yachiyo and others.
Replying to one of the messages, a text back reveals the sender can be found in the Endless Solitude.