Koi-Koi is a traditional Japanese card game played with a set of Hanafuda cards. The game typically involves two players who aim to form specific combinations of cards to score points. Each player takes turns drawing cards and can declare "Koi-Koi" to continue playing for higher points if they believe they can create more valuable combinations. The game is played in rounds, and the player with the highest score at the end wins. Koi-Koi is popular for its strategic elements and is often enjoyed during family gatherings and festivals, making it a significant part of Japanese culture and entertainment.