In my head, pretty much everything in princess tutu has a deeper meaning, and kraehe's outfit is not an exception. At first glance, it's just a reference to Odile the black swan, with classic seductress tones in the stooping neckline, but what if I said that a lot of her story is in that dress?
Are you familiar with the phrase "I hate remembering the things I did to be loved"? That outfit, with context of her insecurities and inner struggles, is the epitome of that phrase. Discarding her humanity, pushing people away, giving herself away, and many more things she did, all for her father's love. All for a love that never existed. The few strips of fabric she wears, leaving her bare and vulnerable, all just to be seen as beautiful. All to not be that crow born into an ugly human body. Do you think Rue wakes up in the middle of the night, lying in pure self hatred and shame? Probably, just like many of us do.
It also symbolizes that she's being used. Used by the Raven, used by Drosslemeyer. Dressed in thorns that tear at her skin, her pain and agony feeds their will. The sacrificial lamb for their goals. They'd sell her for a penny. Trust, I had more to say in my head but I don't know how to put it out well, so just understand what I'm trying to communicate through vibes.
Anyways, Kraehe's outfit is not shameless fan service, it has a deeper meaning than just a reference. My poor sweet daughter.