is the daughter of Rumiko and Kiyoyuki Nonaka and the grand-daughter of Seiko Hata. She is also the younger sister of Rika Nonaka, but she originally existed in a different reality than the older girl. When the varous realities collapsed on each other, she ended up meeting the girl who shared the same family in the end of Book Three.
She is a short, young girl with brown-red hair tightened into a pair of pigtails on either side of her face. She wears a pink shirt and a blue dress, along with pink sandals. She also wears a golden necklace shaped like a nine, indicating she is the Ninth Angel. She is not aware of this yet. She's playful, energetic, and outgoing. She also is curious about the older kids, but Rika is trying to teach her about the concepts of secrets. Kristy is similar to her sister, but seems to lack the sadness and anger that seems to hover over Rika, suggesting that Kristy is how Rika could have been.
She is also the partner to Kudamon. She was able to Biomerge with him in Book Four when he combined with a Royal Knight that was either his future or past version (when the same individual, only from different points in time, encounter themselves physically, they will combine together to form a single individual). She Biomerged with him in order to stop a rampage he began after that event. She hasn't Biomerged since then.