She's a harpy, and the second liminal to live with Kimihito. She has a human body, but halfway down her upper arms they turn into feather-covered wings. She has a free thumb with a claw, so she can use her wings as hands (to some extent). She is good-natured, happy, and playful. However, her attention span is very short. That's why Kimihito called her a "bird-brain". At the extreme, she can forget everything after taking 3 steps.

https://youtu.be/KBfEz4NHjrc?t=38