This is the sword of Aatrox, the Darkin blade, from League of Legends. The model itself was taken from the ingame files, and then re-meshed in meshmixer. The re-meshing removed most of the “polygonical” effects from the model, leaving it with a more worn, skinlike look to it.
The sword itself is about a foot taller than aatrox himself, so for maximum accuracy the pommel of the sword should be about a foot above your head when placed center on your back for cosplay.
I would recommend utilizing a internal support structure with the included “gripless” model, such as a wooden dowel rod or appropriately sized PVC pipe.
The author hasn't provided the model origin yet.