Koi-Koi

Koi-Koi (こいこい) is a popular card game in Japan played with Hanafuda cards. The phrase "koi-koi" means "come on" in Japanese which is said when the player wants to continue the hand.

The object of the game is to form special card combinations called "yaku" from cards accumulated in a point pile. Players can gain cards in their point piles by matching cards in their hands, or drawn from the draw pile, with cards on the table. Once a yaku has been made, a player can stop to cash in points, or keep going (referred to as "koi-koi", hence the name of the game) to form additional yaku for more points. The point values assigned to individual cards have no effect on the score, but they are helpful to judge their value in forming yaku.

An initial dealer (called the "oya", or "parent"), is decided upon when the game starts. This can be done with any method (rock-paper-scissors, dice roll) the players agree upon. A hanafuda-specific method involves random card draw: each player draws a single card; the player who draws a card from the earliest month is the oya. If both players draw a card from the same month, the player with the higher value card becomes the oya.

To deal, the oya deals eight cards to his opponent (face down), the table (face up), then to himself (face down), though this is normally done two or four cards at a time. The rest of the cards are set aside as a draw pile, and then play begins starting with the oya.

On a player's turn, he may match by suit (i.e. month or flower) any one card in his hand with one on the table and take both into his point pile. If he cannot match a card from his hand, he must discard a card face up to the table. After matching or discarding a card, he then draws one card from the draw pile and places it face up on the playing area. If this card matches any card now on the table, he must match that card and take both for his point pile; otherwise, it becomes part of the table. In the event that the drawn card matches more than one card on the table, the player gets the choice as to which card to match and therefore keep in addition to the drawn card.

After a player's turn ends, if he made at least one yaku that turn, that player must then make a choice. He may end the hand and add the value of his yaku to his point total, or he can choose to continue playing (calling "koi-koi") in an effort to gain more points. In some versions, a player may only call koi-koi once per hand; in others, a player may call koi-koi on multiple yaku-forming turns. Calling koi-koi leaves the player vulnerable, as if his opponent is able to form a yaku before the caller forms another, the opponent gains double his score and the caller earns nothing. If a player has yaku totaling 7 or more points when the hand ends, that player earns twice that value. If a player hits 7 or more points and his opponent had called koi-koi, he gets both doubling bonuses for a total of four times his score.

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Wikipedia