Two player riichi mahjong described here is adapted from Fukumoto's Ten. Speed is emphasized over everything else. In the latter stage of a hand, once tenpai is declared the players will adopt an offensive or defensive role. Two-player mahjong is considered a "tenpai prediction battle."
Each player starts with zero points and compete for a pot of one hundred thousand points which are placed aside. The person who has the most points after a one hour period wins.
- Japanese Mahjong Set (x 2). One set is played with the other is set aside for Stage B.
- 100k points
- Alarm clock or timer
- One away from mahjong. This is declared before proceeding to Stage B.
- Tenpai with a closed hand. A player also places 1000 point bet and is privy to the ura dora(s) upon winning.
- Waiting on a tile you previously discarded that would have otherwise completed your hand.
- menzen tsumo
- Self-draw win.
The East and West players should be determined in a random way. They will sit across from one another. The entire round is always east. In other words, the valued wind tiles (kazehai) are East and West.
Roll the dice; this will indicate where the starting hands are dealt from. Upon dealing if South is chosen the West player will deal. Symmetrically, if North is chosen the East player will deal.
A complete game ends after one hour. A warning will be issued twice: at 50 minutes and 55 minutes in the hour. The two players will be prohibited from viewing the clock to prevent stalling (i.e. run out the clock). There are no specified number of rounds. The game continues until the time runs out.
The following rules have been written with the assumption the reader has a general understanding of Japanese mahjong. The game takes place in two stages. In the first stage the game is played similarly to four player mahjong but with instead only two people. Chis are allowed. In the second stage, the normal game ceases and the players take a defensive and offensive role. The defending player may successful prevent the attacking player from winning should he predict the tiles the attacking player is waiting on.
The game continues until 18 turns have gone by or until a player declares tenpai or riichi. If after 18 turns no one declares tenpai or riichi the hand ends in a draw. With an open hand you can declare tenpai. Likewise, with a closed hand you have the option of declaring riichi or tenpai (should you not want to call riichi). Once tenpai or riichi is declared the first stage is over and the second stage commences.
In stage B drawing and discarding tiles cease. The player who did not declare tenpai/riichi (the defending player) will choose two tiles in which he predicts can complete his opponent's hand.
If the guess is correct the defending player prevents the win and the hand is over. The attacking player must reveal his hand to show that he was indeed tenpai.
If the guess is incorrect the player who declared tenpai/riichi (attacking player) is allowed to draw five tiles. If the winning tile is among those five he displays his hand and wins.
If the five tiles that are drawn do not yield a winning tile, the defending player chooses two additional tiles that he thinks can complete his opponent's hand. Again if the guess is wrong, the attacking player draws five more tiles. This is repeated until the defending player chooses the correct tile, the attacking player draws a winning tile, or the wall is exhausted and only the dead wall is left.
If a player draws a tile that can complete his hand but does not want to use it (i.e. forgoes a winning tile for another hand configuration) he lays the tile face down among his discards, passing on the win, and draws another tile after that.
The dealer has an advantage of earning 1.5 times more than the non-dealer. The person who successfully won last hand continues to be dealer. The dealer retains dealership even if his wins are prevented. In other words, the dealership only transfers when the non-dealer wins a hand.
Declaring riichi while in furiten is strictly prohibited even should you draw your winning tile. Declaring riichi/tenpai where there is no possibility of winning (e.g. all waits are amongst the players' discards or melded tiles) is legal.
Ten 1000-point counters are given to each player at the start as a matter of convenience to declare riichi.
At the end of the hand where there is no winner the riichi bets remain in the pot and given to the next winner. Or in case of time running out in which the game ends, the accumulated riichi bets are given to the player in the lead.
In Stage B, a kan can be made if it doesn't change the waits of the hand after riichi has been declared.
If the hand ends in a draw the attacking player must reveal his hand to prove he was in tenpai. After each hand where the dealership does not transfer a 100-point counter is placed. There is no 2-han minimum even if four or more counters are out.
The game ends after one hour. The player with the most points wins.
- Because speed is a priority in the game, taking time to build a big hand will be fruitless if the other player announces tenpai first.
- Calling riichi also yields way to menzen tsumo, an additional yaku. Since five tiles are drawn the likelihood of menzen tsumo is higher.
- Dealer is always in the position to earn more points. The dealer has the advantage of 1) having a double wind; 2) earns 1.5 times more points than the non-dealer.
- In order to prevent another player's win, your opponent can only bases his guesses on the tiles you've discarded and melded. Therefore the players may need to providing discarding tiles that will mislead your opponent in guessing the wrong waits (camouflage).
- Fukumoto, Nobuyuki. Ten. Volume 12. Chapters 102-110.