It Looks anazing!!
Person below isn't..exactly right...It's not a fan costume. It's an official event design for the game Fate Grandorder. Which is part of the Fate series (there are animes but I don't think this design ever shows up in the anime. I haven't watched it, so correct me if I'm wrong) fategrandorder.wikia.com/wiki/…
About game I do not know sorry but yep on anime all fate series this costume not showed😊