Green Grows the Holly, by BT aka Stranger https://archiveofourown.org/works/88984 Klaus goes to Castle Gloria as part of an investigation— an ancient British artefact has disappeared from a museum and Klaus suspects Dorian has stolen it. He finds the Castle’s inhabitants in preparation for a celebration: not of Christmas, but something more ancient.
Cantiques de Noël, by BT aka Stranger http://strangeplaces.net/sylvia/BT/Cantique.htm The Major, mentally exhausted at the end of a mission, is delayed in the UK. He stumbles across a Christmas house-party hosted by Dorian.
Goodwill to All Men, by Karen Colohan aka yavannauk https://archiveofourown.org/works/630485 Dorian gatecrashes a Christmas party that Klaus is holding at the Schloss for his Alphabets. It’s a costume party— and Dorian’s costume is sensational. (Naturally.) Explicit – and hot.
Klaus’s Christmas Carol, by dkwilliams https://archiveofourown.org/works/2805275/chapters/6301649#workskin Based on Charles Dickens’ A Christmas Carol. Canon characters take the roles of Ghosts from Dickens’ story. The “Ghost of Christmas Past” section about Klaus’s unhappy childhood experiences made me cry the first time I read it. The ending, like the ending of Dickens' story, is nice.
Alphabet Soup for Christmas by Cassie Ingaben https://archiveofourown.org/works/27826285 The Eroica team and the Alphabets stage A Christmas carol. The Muppet version.
Silent Night by Kat and Whizzy https://archiveofourown.org/series/1428655 It's just beautiful, highly inspiring, lovely emotion, great details, good angst, nice structure, things like that. My favorite Christmas story is one I've recced several times before, but I'll try to fit it in whenever I can.
Amity33's A Christmas Mess, in which Klaus is forced to spend Christmas at Dorian's castle ... Cute story with everyone well in character and good humor, some good lines and nice descriptions. http://archiveofourown.org/works/1083894
Heather Sparrow's The Fifth Season - Karnival - in the Rhineland area, on Weiberfastnacht, the women rule. Custom have it that women chase a man, cut off his tie and kiss him. G is aiming very high and waits in the office with a scissor. However, Dorian is also in town ... Warm, friendly tone, genuine feeling. http://archiveofourown.org/works/164645
Heather Sparrow's "So how was your weekend". Christopher Street Day parade and Klaus is to provide security. Poor Klaus, what a mission ... http://archiveofourown.org/works/132596