A swallowtail butterfly fairy. But with that said, she doesn't just embody grown butterflies, but also caterpillars and chrysalids; she can be said to be a fairy embodying insect growth, rebirth, and metamorphosis. Like Cirno, she's stronger than usual due to some strange force. She's in berserk mode, basically.
Fairies typically go berserk during most incidents anyway. Her regular personality is extremely gentle-- no matter where a fight breaks out, she'll head over to play. Touhou