Well, i'll be darn Billy Hill, i never expected to have an answer and finaly discovering what kind of asset that piece of clothing was.
Further more, it never occured to me that this "dress" would turn in fact to be a kimono !
I was sure it was some kind of medieval dress or mage/wizard dress going all the way to the floor with long sleeve. I'm flabbergasted, happy and also at the same time a bit annoyed. (Because it turn out in the end it wasn't the type of clothing i thought it was. Buuut, giving how the picture is showing the kimono, i guess my mistake was legitimate.)
Oh well, thank you again Billy Hill for your reply. At least now i know. It was something that was bugging me for a long long time.