Each round you're dealt 8 cards, 8 cards sit face-up on the field, and the rest form a draw deck.

Your turn: play a card from your hand. If it shares a month with a field card, you capture both. If it matches nothing, it stays on the field. Then draw the top deck card and repeat the same matching against the field.

Yaku: certain combinations of captured cards score points (e.g. three "bright" cards, five ribbons, boar+deer+butterfly, etc). The moment you complete or improve a yaku, you choose: Koi-Koi (keep playing for more points, but doubles the round's score if anyone scores again) or Shobu (bank the points now and end the round).

Scoring bonuses: if Koi-Koi was called at all this round (any number of times), the final score doubles once. Separately, if the winning yaku is worth 7+ points on its own, that's another doubling. These two bonuses can combine for up to 4x total, but calling Koi-Koi more than once doesn't multiply the score further.

Highest total score after all rounds wins.