Kotone's Guardian Character is shown with pink hair and a pink eighth note hairclip in her hair, which is pulled up into a bun with a long bang on the right side of her face. Her dress is blue or dark purple with shoes to match. She carries around a white violin and doesn't mention her name in the episode.
As an X-Character, she looks like a typical one, black with a red "X" on their foreheads, but she carries a violin which she uses to create some of her attacks.
After Kotone runs from her father's workshop after her little mistake, Amu finds her in the park when Ran, Miki, and Su sense her heart's egg. Amu and her Guardian Characters get to the park, but are too late when they see Kotone sitting against a lamppost, clutching onto the ruined violin. An X-Egg appears next to her and when Amu notices it, it flies off, but Ikuto, having Character Changed, catches it with Phantom Claw. Yoru tells Ikuto to get rid of it because it wasn't the Embryo, but Amu tells him not to because it was Kotone's heart's egg. Ikuto seems somewhat surprised (he knows Kotone because he goes to her father's violin shop) and looks to Amu to see if it was true, but the X-Egg escapes from his clutches and hatches. Ikuto then notices Kotone sitting off to the side, but doesn't help Amu when she Character Transforms into Amulet Spade to stop the X-Character.
A transparent picture of Kotone appears next to her X-Character and says she wasn't cut out to be a violin craftsman, saying she had no talent. Amu asks her what she was talking about before the X-Character sends an attack powerful enough to knock her off of her feet. Worried, Ran and Su ask Yoru and Ikuto to help Amu, but Yoru tells them they were enemies, causing Ran to call him a lazy jerk.
Kotone appears again and says that even though she had been speaking confidently, she screwed up big time. She says she could never show her face to her father or to Saeko. Amu asks her what was wrong with making a mistake once or twice and tells Kotone she had a dream Amu couldn't imagine since it took a violin a long time (one or two hundred years according to Kotone) before it could produce its rightful sound. Kotone tries to say something, but Amu goes on, saying that when Kotone first told Amu about her dream, she thought she was pretty cool and dazzling. Amu then locks onto her negative heart and purifies the X-Character.
Kotone's Guardian Character, now to her correct appearance, thanks Amu and tells her she had faith in Kotone and that she was sure Kotone would make plenty of violins people years from then would think sounded beautiful. Then she goes back to her egg and enters Kotone, waking her from her trance.