Before I give away that theme, allow me describe the feel of the game. First off, Hanabi is played cooperatively, and it's HARD. It creates a dynamic tension in the group, requiring everyone's best attention and communication skills; there's lots of eye contact and close listening. Your goal as a team is to complete colorful sets of five cards, one card at a time, and each must be played precisely in order. You fail if a card that skips a number, for example, and the game is over on your third failure.
The most unusual aspect is that all your cards are turned outwards, which is to say you can see everyone else's hand but your own. This means you can only determine the correct card to play via information sharing, which is further constrained by the rules: you may spend a token to tell another player ONE THING about their hand, e.g. "you have two 3s". You have eight tokens, and 25 cards to lay down in order. Go.