Mahjong Time is announcing Japanese Mahjong rules for Sit and Go tournaments! Japanese Modern Mahjong rules at Mahjong Time are very similar to Riichi rules, with the following variations:
1. Kuitan - A variation of Tanyao(All Simples or Inside Hand) that in Riichi must be concealed but in Japanese Modern the sets can be melded.
2. Ryanhan-Shibari - When there are five counters on the table, Riichi requires a 2 han(yaku) hand, whereas Japanese Modern requires 1 yaku.
3. Kuikae - When breaking up an existing Chow is not allowed. For example, if you claim a 4 Bamboo, meld a 2-3-4 Bamboo, and immediately discard a 1 Bamboo, players can see that you broke up an existing Chow. And they'll assume you are trying for Tanyao (All Simples). Under the Kuikae rule, you are not allowed to do this, but it's okay to take the tile, make the meld, and discard an unrelated tile on that turn. 1 Bamboo will be inactive for 1 turn and you can discard it on a later turn.