This story, retroactively dubbed "Chapter 16.5," details what happened off-screen during that night in the inn. It is explicit in nature, focusing entirely on the physical consummation of Kirito and Asuna’s relationship inside the floating castle of Aincrad.
There is a notorious full-color doujinshi by the circle “Uchi no Neko” released around 2013 that adapts 16.5 faithfully. Scans of this book are extremely rare due to copyright takedowns. Finding a high-resolution “WORK” of this specific book is the gold standard for this search query. Sword Art Online Chapter 16.5 Full Color WORK
In the original light novel series by Reki Kawahara, the story moves cleanly from Chapter 16 (Kirito and Asuna’s strategic meeting in the inn) to Chapter 17 (the next morning’s breakfast and dungeon raid). The “.5” designation is a fan-made label for a supplementary, adult-oriented short story that Kawahara wrote for a small circle of friends early in the series’ life, long before SAO became a global juggernaut. This story, retroactively dubbed "Chapter 16
