She is another member of the school's photography club, whose specialization- according to her club's term is "stealth photography" which is basically a method used by the paparazzi of taking pictures of people(usually celebrities) caught in awkward moments and not get notice. There is a running gag that the reason she is called "Stealth" is because of her uncanny ability to appear anywhere at anytime and melt away at the same time.

(Source: animefreak)

She has a secret identity as a famous cosplayer Alice-chan.