Sword Art Online: Mother's Rosario - Volume 1 - Paperback

If you thought that playing an MMORPG sounds like fun, you might change your mind about it after reading "Sword Art Online," or SAO for short. In this story, players of MMORPG get stuck in the game but at least several of them manage to play.

Mother's Rosario is actually a side story in SAO. As far as timeline goes, this story happens between the Phantom Bullet and Alicization arcs. 

For those who didn't know, SAO was originally a light novel that was adapted into manga because of its huge popularity. This light novel series has a total of 26 volumes. Mother's Rosario arc is based on the 7th volume.