"At first it was just us falling asleep and never waking up. Billions stuck in fantasies or lost in nightmares. Eventually, some of us showed mastery in dreaming and coming back to life. We gathered around the remains of the old world and started fighting back against the dreams, pulling back those we could save. Many minds and lives were lost in a never-ending uphill war. Then They appeared from beyond the wall of sleep, forcing our/their eyes open and trying to invade our world, through force or subterfuge. The war spilled over." You are a Dream Diver - someone who can still wake up and come back. Your D-goggles, mouth guard, and playlist are your weapons and best friends deep under. Each night you try to dream others back into awakening, surviving yours and theirs deepest subconscious. When asleep, you search and fight for loved ones, friends, random strangers. Every sleeper coming back counts. They're all new recruits. You've dreamed many things, but your biggest fear are the Nightmare Ones, mysterious alien minds who may have started it all. There are not many like you left, but you can't and won't give up. The world must wake up again.
Use any mechanic you want. Be creative. If you want to collaborate on making Oneirica a bigger thing, https://www.reddit.com/user/deadbutsmiling. Finally, don’t forget to wake up - or all is lost… ;-)