The object of this achievement is to get into a game with the 4 characters: Sam B, Logan, Xian Mei, and Purna.
Normally it's pretty rare (in my experience anyway) of finding anyone who is playing as Xian Mei or Purna.
If you cannot find anyone from random games, ask your friends to make a new character (preferably the character that's not currently in the group) and go through the prologue. When they finish you invite them in and get all 4 characters together.
Then you should have your achievement.