It was started by Kinoko Nasu during the production of Fate/hollow ataraxia. He wanted to have DDD directly related to F/ha but that didn't work. It talks about Ishizuka Arika, a guy who lost an arm and has strange experiences concerning demons.
Apparently, it's pretty good.
2/6 vol. released.
Illustrations by Koyama Hirokazu (Type-Moon).