If you haven't checked out Ironsworn before, you must do so. Everything about that game champions the sort of outside-the-box thinking that spurred me to seek systems other than the "Tried & True". My first foray into the system was actually Starforged, a sci-fi offshoot, and that's where I first discovered Truths. In the spirit of my game design forebears, I immediately swiped the idea, filed off the serial numbers, and gave it a fresh paint job.

"Aesir" is an amalgamation of proto-European cultural ideas on the one hand, and a generationally-loved Nickelodeon cartoon on the other. The adult (and often bleak) themes of the former are contrasted starkly by the bright, kid-friendliness of the latter. I also struggled with the fact that some folks would see the "avatar with vikings" notion of the game, and want to include certain... unsavory elements. 'R-rated' elements. Many tables (wisely) address such topics with Session 0 "go/no go" conversations. I wanted a bit more. 

My thought was to use an Ironsworn-like "Truths' discussion to decide what flavors each campaign (called a "Series" of episodes, after the show) should have. I wanted this to accomplish several things:

• Purchase buy-in of the setting from everyone at the table
• Initiate some "go / no-go" discussions
• Ensure that each Series is unique

The Hirds each come with four suggested Themes. Let's look a bit at a Hird of Vanir, who want to destroy the Avatars. For simplicity, let's just look at two of their four suggested Themes and the attendant Truths that a table must choose from: 

Runecasting  -  Who may acquire the power to shape reality?

1. Like playing an instrument, anyone can do it with enough practice
2. Like being a polymath, only the gifted can do it with the right training  
3. You either must or can’t; It is a blessing to some and a curse to others

1. Capricious gods with mortal foibles 
2. A chaotic maelstrom of frivolous sprites 
3. A celestial hierarchy of great and petty beings

Your table chooses one of the options for each Theme to be a Truth for your Series. In so doing, you have shaped the lore and world of Aesir to your whim! A Series depicting a group of Vanir in a world where anyone can be a Runecaster, will play very differently from one where you must be born with it! Further, if the Vanir are concerned with restoring old gods, well, those gods might still be around in Asgard if your table chose the first option from The Spirit World theme. And that's just two of the four themes! 

My hope is that the selection of themes and truths will inspire everyone at the table by creating a more unified vision of the narrative you'll collectively weave throughout the Series. Since you choose your Hird and Truths before you make characters (in accordance with Rule 3, page 40), everyone should have a very clear idea of what the overall story arc is going to cover and can create characters accordingly.