The game seem to take place between season 2 and 3 of the anime. They don't know Sinon, Hebishima's 99th girl and the main girl of Season 3. All the characters minus Suguha escaped from a online game where when you die in the game, you die in real life. Inoha was apparently there too. More recently Asuna escaped from the rapist, Sugou Nobuyuki, the main antagonist of season 2. We see scenes from Kirito's nightmares.
The canon characters are Kirito, Asuna, Kyouko (Asuna's mom), Suguha, Sinon, Alice (one of the random girls from a Screening Room video), and Andrew (Suguha's boss who we never seen). Hebishima, Charlie, and Inoha are all OCs. The dev in a poll asked which canon character Charlie's girlfriend should be. I voted for Lizbeth.