User blog comment:A, Mori/Sub-sessional SFANB/@comment-1827303-20141015154527/@comment-16075172-20141015154745

So, the main group is the group of eight (Hank, Zoshi, PS, LD, Luka, Lazro, Sam, Rev) that connects to each other through the servers, and the sub-sessional characters are minor characters who aren't part of this group but are still a part of the session as a whole. Good to know.