A doujinshi co-authored by Kawahara Reki, under the pen-name of Kunori Fumio, and Kurusu Tatsuya on Sword Art Online.
Note: Part comic/novel doujinshi. Novel by Kawahara Reki, manga by Kurusu Tatsuya.
The contents are:
"The Final Promise"
"A Spot of Sunshine in the Winter"