When the Sensei's lesson is over, the apprentice ninjas meet up in the dojo yard to play an explosive game.

In Boom Bokken, the players split up into teams and pass between them a bomb that must never touch the ground; otherwise it will explode! During the game, players play a card featuring a number between 1 and 8. As they do so, they instruct the next player (designated by them) to play a card that is «higher» or «lower» than the card they have just played. If the designated player cannot play a higher or lower card as called, the bomb explodes and the player is out of the game for the rest of the round. (Cards of identical value can be played.) When a player manages to play all the cards in his hand, he is safe for the rest of the round. The quicker the teams manage to get their players home safe, the greater their rewards.