The fairy tales these characters are cosplaying for are, from upper left, clockwise:

Natsumi: Cinderella, which fits because her adult form is a magical disguise.

Yoshino: Little Red Riding Hood, which also fits because the Angel she can summon is a big bad animal with large ears, eyes, and sharp teeth.

Kotori: The Little Match Girl, fittingly enough for the Angel of Fire that Kotori can summon.

Miku: The Little Mermaid, whose story is similar to how Miku lost her own voice in her backstory.

Thanks, I couldn't figure out Yoshino in this one.