Random Curiosity's Bakamochi: "Well, just in case anyone was about to forget about it, Guilty Crown returns with this 11-minute OVA after a season and a half after its finale. The short is essentially an extended teaser to the VN Guilty Crown: Lost Christmas by Nitro+, and hence explains very little about the premise. The bulk of the content in terms of the “plot” are in the trailers instead, and frankly, Lost Christmas is what the original should have been."
