Koi Koi is a traditional Japanese card game played with a deck of Hanafuda cards. The game typically involves two players who aim to collect sets of cards to score points. Players take turns drawing cards and can declare "Koi Koi" to continue playing for higher points if they believe they can form more sets. The game is played in rounds, and each round ends when a player reaches a predetermined score or when all cards have been played. Koi Koi is known for its strategic elements and is often enjoyed during family gatherings and celebrations in Japan.