Any ideas on what this is?
Show it again without the marks?
Looks like some sort of headpiece to me. Maybe the girl took it off after the battle was over.
EDIT: Yeah, search for "The Guardian Legend" on Google Images and you'll find several (not necessarily official) pictures of the girl wearing it.
Thanks tokumaru, I see it now! Didn't know what the headpiece looked like, aside from the few pixels on the in-game sprite. Mystery solved.
Congratulations on being the greatest player!