Koi-Koi

1 Overview & History

Koi-Koi is the most popular game played with Hanafuda (花札, "flower cards"), a traditional Japanese card set. Hanafuda has been part of Japanese culture since at least the late Edo period (1600s–1800s). Its origins trace to Portuguese playing cards brought to Japan, which were eventually transformed into the uniquely Japanese floral format.

Perhaps most famously in the West, Nintendo began as a Hanafuda manufacturer in 1889 — Fusajiro Yamauchi founded the company to make handcrafted Hanafuda cards. Nintendo still sells Hanafuda today. The transition to electronic games came nearly a century later.

Koi-Koi is a 2-player capture game where both players race to collect specific combinations of cards (yaku) from a shared field. The core decision — "koi-koi" (continue for more) vs. stopping to collect — creates the game's elegant tension.

2 The Hanafuda Deck

48 cards, 12 suits of 4 cards each. Each suit represents a month and a flower:

3 Card Types

• Bright (光, Hikari): 5 cards — the highest value cards. January Crane, March Curtain, August Moon, November Rainman, December Phoenix.
• Animal (種, Tane): 9 cards — picture cards with animals and objects. The September Sake Cup is sometimes treated as a special Animal/Bright hybrid.
• Ribbon (短冊, Tanzaku): 9 cards — cards with colored ribbons. Three types: Red with writing (Poetry Ribbons), Blue (Blue Ribbons), and Plain Red.
• Chaff (カス, Kasu): 24 cards — plain cards with no special features. Lowest value individually but needed in bulk for the Chaff yaku.

4 Deal & Setup

Shuffle the 48-card deck. Deal 8 cards to each player. Deal 8 cards face-up to the center field. The remaining 24 cards form the draw pile face-down.

If 4 cards of the same month appear in the field at deal, redeal. If all 4 cards of a month are in one player's hand, that player may declare an instant win (Teyaku) depending on variant rules.

A full game consists of 12 rounds (one per month). The dealer alternates each round. Track scores across all 12 rounds; highest total wins.

5 Playing a Turn

Each turn has two phases:

Phase 1: Match from Hand

Play one card from your hand face-up onto the table.

• If it matches a field card by month: Capture both. Place in your capture pile.
• If two field cards match: Capture all three (your card + both field cards).
• If no match: Your card remains on the field.

Phase 2: Flip from Draw Pile

Flip the top draw pile card.

• If it matches a field card: Capture both.
• If two field cards match: Choose which one to capture (take both the flipped card + one field card). The other stays.
• If no match: The flipped card stays on the field.

Check for Yaku

After your turn, check if you've completed any yaku. If you have, you must declare Koi-Koi or Stop.

6 All Yaku (Scoring Hands)

Bright Yaku (光)

• Five Brights (五光 Goko): All 5 Brights — 10 pts (15 in some variants)
• Four Brights (四光 Shiko): Any 4 Brights not including Rainman — 8 pts
• Rainy Four Brights (雨四光 Ameshiko): Any 4 Brights including Rainman — 7 pts
• Three Brights (三光 Sanko): Any 3 Brights not including Rainman — 5 pts

Animal Yaku (種)

• Boar-Deer-Butterfly (猪鹿蝶 Inoshikachou): July Boar + October Deer + June Butterfly — 5 pts
• Sake Cup (月見酒 Tsukimizake): August Moon Bright + September Sake Cup — 3 pts (some variants only)
• Hanami-zake (花見酒): March Curtain Bright + September Sake Cup — 3 pts (some variants)
• Tane (Animals): 5 or more Animal cards — 1 pt for 5, +1 for each additional

Ribbon Yaku (短冊)

• Poetry Ribbons (赤短 Akatan): All 3 Poetry Ribbons (Jan, Feb, Mar) — 5 pts
• Blue Ribbons (青短 Aotan): All 3 Blue Ribbons (Jun, Sep, Oct) — 5 pts
• Tanzaku (Ribbons): 5 or more Ribbon cards — 1 pt for 5, +1 for each additional

Chaff Yaku (カス)

• Kasu (Chaff): 10 or more Chaff cards — 1 pt for 10, +1 for each additional

Multiple yaku stack — score all combinations you've completed simultaneously.

7 The Koi-Koi Decision

When you complete a yaku after your turn, you must immediately declare:

• "Koi-Koi!" (こいこい — "come on!"): Continue the round. You're betting you can score more before your opponent completes a yaku or the round ends. Your score potential increases, but so does the risk.
• "Stop" / "Shobu" (勝負 — "settle it"): End the round now. Collect your current point total.

Consequences

• If you call Koi-Koi and later Stop: your score is doubled (×2).
• If you call Koi-Koi and your opponent then completes a yaku and calls Stop: your opponent's score is doubled — and you get nothing. The risk cuts both ways.
• If the round ends with cards exhausted and no one has stopped: no points are scored for the round.
• If you call Koi-Koi and then complete another yaku: declare again. You can continue calling Koi-Koi, accumulating both score and multiplier risk.

In some variants, scoring 7+ points (multiplied or base) doubles the payout to the opponent. This creates extreme tension when both players are close to high-value yaku.

8 Scoring & Payment

The winner of each round scores points equal to their completed yaku total (modified by Koi-Koi multiplier if applicable). Over 12 rounds, tally cumulative points. The player with the most points after all 12 rounds wins the game.

In chip/money play: the loser pays the winner an amount equal to the round's point score. Some groups double payment if the winner scored 7+ points.

Teyaku (手役): Special hands dealt at the beginning of a round can result in instant wins or bonus payments depending on house rules. Common teyaku include holding 4 cards of one month, all chaff, etc.

9 Strategy

Prioritize High-Value Yaku

Bright yaku (especially Three Brights and Inoshikachou) are worth the most points. Pursue them deliberately rather than grabbing every available capture.

When to Call Koi-Koi

Koi-Koi is correct when: (a) you're close to another yaku and your opponent has few captures; (b) you're behind and need to multiply; (c) the round is early with many cards left. It's wrong when: your opponent is also close to completing a yaku — they'll stop before you can.

Deny Opponent Yaku

Sometimes the best play is capturing a card your opponent needs, even if it doesn't help your own yaku. Track what your opponent is collecting — if they're one Bright away from Three Brights, prioritize denying that Bright over building your own ribbons.

The Sake Cup

The September Sake Cup is a special Animal that participates in two drinking-themed yaku (Hanami-zake, Tsukimizake). Players who hold it have flexible yaku paths — an opponent with the Sake Cup should be watched carefully.