The trio of Miina, Nachan and Ayumin, formed last year, are supposed to exist only as drawings of the group’s illustrator, Yuritan. The three are only some of the characters found in the accompanying manga. Apparently members can be erased for bad behaviour.
Their music is a mellow electric/accoustic styling that doesn’t break a lot of new ground but has a decent tonal base. It has just enough of an interesting blend of effects with vocal phrasings just unique enough to set it apart from mainstream jpop.
But the music might not be the point of this project — Sayonara Ponytail might be more about being part of the larger project the manga represents.