I run weekly gaming sessions, with variable players. As a result, we play single-session, zero-prep, no-GM, story-games. I've been told that Polaris: Chivalric Tragedy at Utmost North is great for that, but it has a lot of backstory for something that's only supposed to be played for 3 hours.

The rules are fairly simple, but they are not written in the order they're encountered. If it were just the rules, I could re-order them in my head, beforehand. But the game relies on the background, extensively. The characters aren't even human, or any other popular fantasy or sci-fi race that can be introduced with a single word. The setting is in the north pole, and everything is made of ice. It's a lot to take in for a simple 3-hour session.

Given that I'm probably going to be teaching the game every time we play it (we have new players almost every week, and not everyone comes every week), how can I quickly convey the background and rules?