It's a kimono.

With a different take.

It's an adaptation of a kimono worn under a kappogi. This is how Ms. Hiroko wears it:

Photo via here

And this is how the model with the adapted top:

The back of the collar stays true to the traditional kimono collar

Kimono and kappogi in one layer

nooy S/S '09 collection
photos via www.nooy.jp