Kaiten Muten-maru is a collectible card game created by the Japanese revolving sushi chain Kura Sushi, beginning in December 2007. The game's mascot, Mutenmaru, is a young sushi-loving samurai hero who serves as the face of the chain's promotional webcomic and card series. Card packs of four cards were sold at Kura Sushi restaurant locations for fifty yen each, with no starter deck required, as play was possible with a small number of cards. This low barrier to entry made it effective as a promotional tool for young customers. The rules and card templates were revised on several occasions across the game's run, which spanned at least two seasons totaling fourteen parts. Because the game was sold exclusively through Kura Sushi restaurants in Japan, it never appeared on general retail channels and had no international distribution. The game's scarcity makes even previously-owned singles difficult to locate. A separate collaboration set was released in 2014 as Extra Pack 3 for the Z/X: Zillions of Enemy X trading card game, featuring Mutenmaru characters in a fully independent format.
Source: tvtropes.org/pmwiki/pmwiki.php/Webcomic/KaitenMutenmaru