As I mentioned in the tags, this is supposed to be a seiyuu joke, with Hinagiku wearing the same outfit worn by the Sky Girls character that Itou Shizuka (Hinagiku's seiyuu) voices (which happens to be a blue outfit).
TnAdct1 said: As I mentioned in the tags, this is supposed to be a seiyuu joke.
Yes, I knew that it was a seiyuu joke, but I still think the artist could have picked another character of Itou's with hair and eyes more fitting for this outfit.