One Unique Thing
From the 13th Age SRD:
Obviously the One Unique Thing (OUT) is a fairly light mechanic. It doesn't rely on other parts of the 13th Age rules, or even the 13th Age setting. This means that the OUT is perfect to co-opt into other games as it will not impinge on systems or settings. It's worked so well for me thus far that I will probably always use it in any game I run in the future.One Unique ThingYour character’s One Unique Thing (their unique) is a special feature invented by you, the player, which sets your character apart from every other hero. It is a unique and special trait to your player, and markedly unusual. The intent is that it provides a special flavor to the campaign and can assist the GM in determining how your character can interact with characters and story in the campaign.Your character’s unique should not provide general practical value in combat. That is not the intent. The intent is to open up story arcs and fun roleplaying opportunities.
What's it do though? What it does do is provide additional depth to both character and setting completely within the hands of the player and GM. It allows the player to add something to their character that is entirely special. It enables the player to direct the game-world and possibly the longer campaign in a way that interests them, by suggesting people, places, things, event, or the like that relate to their characters. It also provides ways for the GM to hook players based on that relationship.
An example from my current game:
I am the only person to ever leave the Dome of Mysteries alive.It's a simple enough statement. It relates directly to a location in the city of Qi in the Numenera game which is the locale that I had agreed with the players where we would set our story. It told me that the Dome would be something I would need to think about using, and not simply a named landmark that might get ignored.
It also told me a little about the Dome itself. If that character is the only one who has left the Dome alive it implies that she is the only character to have left the Dome at all (though I was tempting to have the building dump dead bodies into the street, this felt far more interesting). As a result nobody in Qi knows what lies beyond the threshold of the Dome of Mysteries, truly making the building's interior a mystery.
I asked my player if she wanted to help determine what was inside and she replied that she wanted no memory of her life prior to exiting the Dome. The mystery just deepened. Now I had a Stealthy Jack who Murders, who had no memory of her past, and is the only person to have exited the Dome of Mysteries, alive or dead.
I ultimately settled on an explanation of what the Dome is, and what happened to my game's intrepid Jack. It has shaped the campaign and with the other players' OUTs my game has taken on a depth and player involvement that would have been more difficult to achieve on my own. I think that the addition of the OUT has proven entirely successful, and feel fully justified in including it in future campaigns I run and suggesting that other GMs consider its use in their own games.