This Christmas is a story written by Yamanashi Moe. It ran in Issue 28 at http://s2b2.livejournal.com/163443.html, and is mirrored at http://www.shousetsubangbang.com/mirror/this-christmas/.
From the author: "One of Pat's co-workers is secretly living in the back of the store. It's none of his business, though. Really."