Kasai is a young kitsune, or mystical fox, in the early stages of her lengthy lifespan. Because of the way they age, she looks as if she is still in her pre-teens, despite being just over 200 years old, spiritually, though her actual age in human years is 20. She can shift into a feral form, bearing the same fur colors, but cannot shift into any kind of anthro form on her own for very long, as that is typically reserved for Celestial Foxes in her tribe. She has two tails, and the second tail grants her the power of kitsunetsuki, literally fox possession, on the willing or weak-minded. She has an affinity with the fire element, and can create, extinguish, or manipulate any non-magical flame at will, as well as remain free from harm from all natural fire as well as most magical fire, and become as flame herself and conceal herself within them.

Her personality varies. She is often shy and unsure of herself, but also passionate at times. Always playful, and frequently mischievous, she loves to play tricks, which often consist of her stealing some bauble under someone's nose, watching them flounder when they go looking for it, and then clandestinely returning it as if it had never moved. Targets of her tricks include watches, glasses, and ladies' underwear in the bath.