It was revealed in the anime that Orihara Izaya actually possesses Celty Sturluson's head, which is also his main motivation for starting gang wars. Izaya wanted to “awaken” the sleeping Dullahan’s head by throwing the world around her into chaos; in hopes that he will be taken to the warrior heaven of Valhalla. He believes Celty is a Valkyrie, a Norse angel of death who chooses which warriors die in battle in order to take them to Valhalla.
Impressive cosplay! I love the pose and the attitude, although I’m not entirely sure how in character the cosplayer is since I’m not familiar with the series. Thanks to Patty for sending this!