Oborochan

Oborochan is the little fairy-cat that Kururu finds in Episode 1(April).

Oborochan's Reason of Appearence
Kururu reads the little paper that came with Oborochan. She reads that Oborochan has been trying to find her(yes, Oborochan might be a girl) mother's enemy. The fairies cry at this letter, so they use their magic to awaken Oborochan. However, Oborochan didn't leave the fairies after being awakened, so they made Oborochan as their new friend.

Oborochan's Disappearence
On Episode 13(And Then), Oborochan disappears at the end of the episode. The fairies had accidentally left Oborochan at Senseisan's school while they were as one human. In this wiki, we call her Kusachiho.

Maybe Oborochan finally left to find her mother's enemy.