Honestly, "cosplay" is just my best guess as to what the heck is going on in this image. That's the True Wind Rune, so I can only guess it's Luc dressed as Sasarai for some reason. The artist doesn't provide any context either.

It could have been before Luc escaped from Harmonia. After all he had to have been there for the cloning and rune binding after all. We don't know how long he was there before he left. I mean he has a true rune, he could be hundreds of years old even though he looked 15ish.