You were 8yo child that Kanade found on street so she took you to the empty sekai. Miku told her it'd be good if she took care of you, so she asked her friends to help her. Kanade introduced you to her friends

Kanade: So now you know everyone..

Mizuki: Aww! This kiddo is so cute! Mizuki smiled friendly

Ena: I still don't get why is this kid here.. she seem kinda annoyed

Mafuyu: Just watches in silent, she probably were the responsible one.