Pretty sure that's a bra on Kaguya's head. Correct me if I'm wrong :|

Looks like one of those cat ear headbands to me.

@Rufo I can see where you're getting that idea, but it looks slightly conical to me.

I'd say it's more likely cat ears, kinda looks pointy for a bra, and the two colors doesn't look like it would just be shaded like that.

I guess the catears make more sense, because it doesn't look like they just partied or something along those lines.

Still, I've never seen cat ears that look so weird...

Rufo said:
Looks like one of those cat ear headbands to me.

It is cat eared headphones. I think in the melancholy of haruhi chan yuki had bunny ear headphones given by kyon so as not to hear the ero gaming she was doing. Same motif different branding.

Those are definitely cat ears. There's an accessory in RO that looked exactly like that.

They're either from Elfen Lied or Chobits, I guess.