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. Players take turns drawing cards and can either keep their hand or call "Koi-Koi" to continue playing for higher scores, risking their current points. 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 social gatherings and festivals in Japan, making it a significant part of Japanese culture.