Koi-Koi [こいこい or コイコイ] is a popular hanafuda fishing game for two players, who compete to capture cards from the table and form scoring combinations known as yaku.
Its name comes from its gameplay element that allows players to decide whether to continue the round (by calling “koi-koi!” [来い来い - こいこい, lit. “come on, come on”]) and risk their points for the chance to improve their score, or end the round (by calling “shōbu!” [勝負 -しょうぶ, lit. “game” or “match”]) and keep the points they currently have.
Koi-Koi is among the best-known hanafuda games outside of Japan, courtesy of its representation in numerous anime and video games.
This game may have developed as a simplification of the Korean game of Go-Stop, which features similar scoring and the same risk-taking gameplay mechanic. (Link)
However, Korean scholars usually consider Go-stop as a derivative of Koi-Koi. (Link 1, Link 2)
A word of caution: As one of the most popular hanafuda games, Koi-Koi exists in a truly huge range of variations, above and beyond most of the other games on this site. Indeed, it may be no exaggeration to say that there are as many house rules as there are houses!
As such, don’t be surprised if the version here differs from what you may be used to. Many of these variations are collected at the end of the page.
¶ Setup
Game setup involves choosing a dealer - 親 [おや, oya], shuffling the deck, and distributing the initial cards.
A decision must also be made as to how long the game will last - 12 rounds is traditional, though other common options are 6 rounds, 3 rounds, or as many rounds as it takes for one player to reach 50 points total.
Conventionally, each round corresponds to a month of the year; the first round is January, the second February, and so on. 12 rounds is thus a year, 6 rounds a half-year, and 3 rounds a season.
Any other house rules should also be established at this point, in order to keep gameplay smooth and fair.
¶ Choosing the Dealer
There is no required method for selecting who is the first dealer, though a typical method in hanafuda games is to shuffle the deck and have both players draw one card each. The player who drew a suit for the earliest month becomes the dealer. If both players drew from the same suit, the player drawing the higher point card becomes the dealer. In cases where there is a tie, this process can be repeated.
The winner of each round becomes the dealer for the next round.
¶ Distributing the Initial Cards
The dealer shuffles the deck, and their opponent cuts. Then, eight cards are distributed to each player, and eight to the table. While there is no required method for this distribution, it is common for the dealer to give four to their opponent, four to the table, four to themselves, and then repeat. Sometimes this is done in packets of two instead of four.
The remainder of the deck is placed face-down to form the draw pile.
¶ Checking for Lucky Hands
After the cards are dealt, each player checks if they possess any lucky hands, or teyaku [手役 - てやく]. There are only two Lucky Hands in Koi-Koi:
- Four of a Kind [手四 - てし, teshi]: All four cards of any given month.
- Four Pairs [喰付 - くっつき, kuttsuki]: Four pairs, a pair being two cards of the same month.
If a player holds one of these lucky hands, then they declare it. That player immediately wins the round, scoring 6 points and becoming dealer for the next round.
If both players hold a lucky hand, then the round is a draw. Nobody scores anything, and the next round begins with the same dealer.
If either of these lucky hands are dealt to the table, then a misdeal is declared. The cards are thrown in, re-shuffled, and re-dealt.
Sources are vague on what should happen if a player holds both of the lucky hands. In some descriptions, they only score 6 points, but in others, the hands stack, and they score 12 points. Decide on this as a house rule before playing!
Despite the name, these ‘lucky hands’ are actually very poor when it comes to capturing cards. The points earned from them are compensation for bad luck!
¶ Gameplay
Each round, the dealer is the first to play. Turn to play alternates.
¶ Turns
On their turn, a player chooses a single card from their hand and plays it to the table.
- If it belongs to the same month as another card on the table, then the cards match, and this matching pair is moved to the player’s score pile.
- If the played card matches with two cards on the table, then the player may choose which one they capture.
- If the played card matches three cards on the table, then all three are captured along with the played card (this is to prevent cards from becoming ‘stuck’ on the table and unable to be captured). To help in recognising this case, three cards of the same month on the table are often collected into a small pile at the beginning of the round.
- If the played card does not match any card, then it remains on the table, and may subsequently be captured by other played cards.
If a card is played that matches something on the table, then the player must capture, as described above. However, there is no obligation to play a card that matches something, even if the player has one in their hand; they may, if they wish, elect to play a card that matches nothing on the table.
As is typical of hanafuda games, each player’s score pile should be kept face-up and laid out on the table, so that its contents are fully visible to all players. Ideally, the cards should also be arranged by type (Brights, Animals, Ribbons, and Chaff) to make detecting yaku easier.
After a card has been played from their hand, the player takes the top card of the draw pile, turns it face-up, and immediately plays it to the table in the same fashion.
¶ Checking for Yaku
After playing both their cards - one from their hand, and one from the draw pile - the player checks their score pile for yaku [役 - やく], or scoring combinations; a list of these is given further down the page.
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If the player has either formed a new yaku, or improved an existing one, then they have the choice to either end the round by calling shōbu, or to continue in pursuit of a higher score by calling koi-koi.
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If they have not, then their turn simply ends, and turn to play passes to the opponent.
¶ Calling “Koi-Koi”
If the player declares koi-koi, then the round continues. Their turn ends, and turn to play passes to the opponent. This is a calculated risk; continuing the round allows the opportunity to capture more yaku, but forfeits all points should the opponent win first.
In many rulesets, each player may call koi-koi as many times as they desire during the round.
¶ Calling “Shōbu”
If the player declares shōbu, then the round immediately ends, and scores are calculated. This is a safe bet, which allows the player to immediately cash in on their yaku.
¶ End of Round and Scoring
The round ends when either a player calls shōbu, or when both players run out of cards in their hands.
¶ Exhaustive Draw
If both players run out of cards in hand without calling shōbu, the round ends in an exhaustive draw, and neither player earns any points. Note that captured yaku are not scored for; if a player called koi-koi but did not subsequently improve their yaku and call shōbu before the cards ran out, then their points are forfeited.
The round is considered over, and the next round begins with the same dealer.
¶ Scoring for Yaku
Otherwise, the player who called shōbu calculates the total point value of all the yaku in their score pile. This total is their base score. Two multipliers are then applied:
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If the player’s base score is greater than or equal to 7, then their score is doubled.
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If their opponent called koi-koi at any previous point during the round, then the player’s score is doubled. (The exact number of times the opponent called koi-koi has no effect.)
The player’s total score is then their base score, times any multipliers they may have earned.
Note that only the player who called shōbu earns any points. Their opponent scores nothing for this round.
The player who called shōbu is the winner of the round, and becomes the dealer for the next.
¶ End of Game
Depending on the terms agreed upon during setup, the game ends after a certain number of rounds, or once a target score has been reached. If playing a certain number of rounds, the player with the greater score at the end of the last round is declared the winner. If playing to a target point total, the first to reach that score is the winner.
¶ Yaku
There is great variation in the possible sets of yaku in Koi-Koi. Some yaku may be house rules, while others are common to nearly all rule sets. In many cases, the point values of these yaku will change depending on source.
The yaku given here are fairly typical of modern forms of the game, as seen in video games and Nintendo’s current Koi-Koi rules leaflet. They are sorted into groups. All of the yaku within each group (except Other Yaku) are mutually exclusive; a player only scores for their most valuable yaku in each group.
For example, if a player has all five Bright cards, they only earn points for Five Brights. They do not earn points for Four Brights, Rainy Four Brights, or Three Brights. This goes for each grouping.
| Points | Yaku Name | Composition |
|---|---|---|
¶ Bright Yaku |
||
| 15 | Five Brights 五光 [ごこう, gokō] |
     15 is the most common value of this yaku, though Nintendo’s rules list it at only 10 points. |
| 8 | Four Brights (Dry 4) 四光 [しこう, shikō] |
|
| 7 | Rainy Four Brights 雨四光 [あめしこう, ameshikō] |
plus 3 of: |
| 6 | Three Brights 三光 [さんこう, sankō] |
Any 3 of: 6 is the most common value of this yaku, but Nintendo’s rules list it at 5 points. |
¶ Animal Yaku |
||
| Points | Yaku Name | Composition |
| 5 | Boar-Deer-Butterfly 猪鹿蝶 [いのしかちょう, inoshikachō] |
   This yaku is worth 1 extra point for each additional Animal card. |
| 1 | Animals タネ [たね, tane] |
Any 5 Animal cards. This yaku is worth 1 extra point for each additional Animal card. |
¶ Ribbon Yaku |
||
| Points | Yaku Name | Composition |
| 10 | Poetry+Blue Ribbons 赤短・青短の重複 [あかたん・あおたんのちょうふく, akatan - aotan no chōfuku] |
      This yaku is worth 1 extra point for each additional Ribbon card. |
| 5 | Poetry Ribbons 赤短 [あかたん, akatan] |
This yaku is worth 1 extra point for each additional Ribbon card. |
| 5 | Blue Ribbons 青短 [あおたん, aotan] |
This yaku is worth 1 extra point for each additional Ribbon card. |
| 1 | Ribbons 短冊 [たんざく, tanzaku] |
Any 5 Ribbon cards. This yaku is worth 1 extra point for each additional Ribbon card. |
¶ Other YakuNote: This group is not mutually exclusive. All these yaku stack with each other! |
||
| Points | Yaku Name | Composition |
| 5 | Flower Viewing Sake 花見酒 [はなみざけ, hanami-zake] |
 |
| 5 | Moon Viewing Sake 月見酒 [つきみざけ, tsukimi-zake] |
|
| 4 | Cards of the Month 月札 [つきふだ, tsukifuda] |
All 4 cards belonging to the month of the current round. For example, all four January cards in the first round, all four February cards in the second round, etc. This yaku is typically only used in full 12 round games. |
| 1 | Chaff カス [かす, kasu] |
Any 10 Chaff cards. This yaku is worth 1 extra point for each additional Chaff card. For the purposes of this yaku, the  Sake Cup also counts as Chaff! |
¶ Variations
As previously mentioned, Koi-Koi is utterly abundant with rules variations; every table has their own way of playing the game. There are most likely far more than we could ever hope to list here, although that isn’t going to stop us from trying!
All of the following rules can be applied or not, depending on your tastes. See which ones you like, and blend them together to make your own version of Koi-Koi.
¶ Setup Variations
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Four of a Kind are Four Pairs are not lucky hands for a player, but instead constitute a misdeal, the same as if they were dealt to the table.
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Four Pairs on the table is not considered a misdeal.
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Four of a Kind on the table is not considered a misdeal. Instead, the dealer immediately captures these four cards, and deals four more to the table to replace them. Alternatively, the dealer immediately wins the round and scores 6 points.
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Each player is dealt 10 cards to their hand, instead of 8.
¶ Older Yaku
The yaku given in the body of the page are typical of modern sources. Slightly older descriptions instead give the following, mildly different treatment of Ribbon and Animal yaku, which some may find easier to work with.
The Bright Yaku and Other Yaku remain the same in this system. The changes in the Ribbon Yaku and Animal Yaku are as follows:
- Boar, Deer, Butterflies is not worth extra points for additional cards. Instead, it can stack with the generic ‘Any 5 Animals’ yaku.
- Poetry Ribbons and Blue Ribbons are not worth extra points for additional cards. Instead, they can stack both with each other, and with the generic ‘Any 5 Ribbons’ yaku. Poetry+Blue Ribbons is not a separate yaku, but instead exists as the combination of Poetry Ribbons and Blue Ribbons.
Even older sources tend to lack many of the typical yaku. Nintendo’s 1960’s Koi-Koi leaflet lacks Boar Deer Butterflies and both the viewing yaku, while Hanafuda - The Flower Card Game additionally lacks Three Brights and Rainy Four Brights. Point values also differ drastically in these old sources.
¶ Taming the Sake Cup
Anyone who’s played Koi-Koi for any length of time will quickly pick up on how overpowered the Sake Cup is. This humble card contributes to no fewer than four different yaku! Unsurprisingly, many house rules exist with an eye to curbing its power.
- The Moon Viewing and Flower Viewing yaku are simply not recognised. (Many video game adaptations will give the option to toggle these yaku on or off.)
- Moon Viewing and Flower Viewing are only recognised if the player additionally owns at least one non-viewing yaku.
- If any November
Willow cards are on the field, then the Flower Viewing is rained off and is not valid. If any December 
Paulownia cards are on the field, then the chilly weather leads to fog, which ruins the Moon Viewing. These cards must be captured and cleared off the table in order for the relevant yaku to count. - The Sake Cup can count as an Animal card or a Chaff card, but not both.
- The Sake Cup only counts as an Animal card, and not Chaff.
¶ Additional Card Properties
- The November Lightning card functions as a wild card, capable of matching with any other card. See the rules for Roppyakken or Mushi for details on how this might work.
- As a variation of the above: The Lightning card only functions as a wild card if any August
Susuki Grass cards are dealt to the field at the beginning of the round, as the warm summer weather presages a gathering storm. - The Sake Cup, Lightning, and/or Yellow Paulownia each count as 2 Chaff cards.
¶ Turn Structure Variations
- Once both players have run out of cards, they may continue the round by taking turns to play a card from the draw pile, until the draw pile is exhausted as well.
- The players draw a card from the draw pile at the beginning of their turn, then play two cards from their hand.
- If the card turned up from the draw pile does not match anything on the field, then the player takes it into their hand, and plays a second card from their hand in its stead.
¶ Draws
- When the game ends in a draw - either an exhaustive draw, or due to both players holding lucky hands - the dealer scores a number of points (typically 1 or 6) and remains dealer for the next round. This is known as dealer’s privilege [親権 - おやけん, oya-ken].
- When the game ends in a draw, the role of dealer passes to the other player for the next round, as opposed to staying with the current dealer.
- When the game ends in an exhaustive draw, the last player to form or improve a yaku obtains their yaku scores, and becomes the dealer for the next round.
¶ Calling Koi-Koi
- Borrowing from Go-Stop, a player may be required to possess at least 3 points’ worth of yaku before they can call koi-koi. If they do not, then they automatically call shōbu. This minimum may vary at the players’ discretion.
- A player may only call koi-koi if they have formed a new yaku; improving an existing one does not count.
¶ Scoring Variations
¶ Multipliers
- The scoring player earns a
x2multiplier if they called koi-koi, not if their opponent did. - The scoring player earns a
x2multiplier if anyone called koi-koi during the round. - The scoring player earns a multiplier equal to the number of times koi-koi was called, plus 1. If their opponent called koi-koi once, they earn a
x2multiplier. If the opponent called koi-koi twice, they earn ax3multiplier, and so on. - The
x2multiplier earned for having a base score of at least 7 originated as a house rule before it was widely incorporated into the game, and some tables may still prefer to play without it.
¶ Zero-Sum Scoring
- Some play with a zero-sum scoring system, in which any points earned by the winner are subtracted from the loser’s score. This helps to facilitate gambling.
¶ Field Multipliers
- Similarly to Hachi-Hachi, if a Bright card is dealt to the field at the beginning of the round, then the score for that round is doubled.
- As an extension of this, if two Brights are dealt to the field, then the score is tripled. Three Brights, quadrupled, and so on. (The multiplier is equal to the number of Brights, plus 1).
¶ Yaku Counting
- The scoring player only scores for their single most valuable yaku.
- The scoring player scores not only for their own yaku, but also their opponent’s.
¶ Bibliography
(todo: pretty this up)
- Hanafuda Games, from IndianWolf Studios
- Hanafuda - The Flower Card Game, compiled by Japan Publications, 1970
- https://web.archive.org/web/20051125014910/http://hana.kirisame.org/koikoi.html
- https://en.wikipedia.org/wiki/Koi-Koi
- Nintendo’s Koi-Koi rules leaflets (both the current one and the blue 1960’s one)
- Innumerable threads on the Hanafuda Reddit where people have discussed their own house rules!
- https://japanplayingcardmuseum.com/005-hanacarta-korea-hwatu/
- https://www.joongang.co.kr/article/2893044
- http://tbs.seoul.kr/news/newsView.do?seq_800=10242335&typ_800=12