While Sao is happening there is an untold story of a game called Chaos Kill Online. It is in alliance with Sword art online. To beat Cko you must beat Sao. And to beat Sao you must beat Cko. 2 friends and a new approacher embark on a journey in Cko determined to defeat cko, only to lose their memory of all of it.

Two brothers lost their mom from cancer and there Dad died with no explanation but they find out he was really killed by the things that haunt the world called Ghouls, angry with the ghouls they set out to find the one that took their father and have a tragic accident along the way.