A magical girl and the secondary antagonist who has a close relationship with Oriko.
The extra chapter Noisy Citrine reveals more details of her past. Originally a cheerful girl, she became antisocial, timid and quiet after being betrayed by her best friend.
Some time later, she met Oriko, so Kirika wanted to be more worthy of the girl's attention by being a different kind of person. This led Kyubey to grant her a more outgoing personality. Her current personality is the result of her wish, which was to "change" herself.
(Source: Puella Magi Wiki)