Hmm... Nanaka, or Asami? Without spoiling, I'll say it seems to make more sense as Asami. Also, that pink line up top might be a little bit of her hair ribbon. sakurasakura hadn't done enough M;Y for me to be sure.

The hair colour matches Nanaka but Asami's black hair wouldn't show up on a black background and I think the style looks more like Asami's as well.