Under the River

What is Under the River in Japanese Mahjong?

Under the River is a one-han yaku in Japanese Riichi Mahjong. It is awarded to a player who wins off the very last discard made during a hand. Under the River grants one han for winning on the final discard of the hand. While inherently reliant on the game reaching the very last discard without a prior winner, it can swing the outcome dramatically, especially when combined with other yaku. Keeping track of who might be in tenpai and discarding carefully on the last turn are crucial defensive strategies to avoid enabling a Under the River win.

How to Achieve Under the River？

Last Discard in the Round: As the wall nears exhaustion, each player eventually reaches the final tile in circulation. If the final discard of the hand is claimed for a win, the winner earns Under the River.

Open or Closed Hand: This yaku does not require your hand to be concealed. Whether your hand is open or closed, you still qualify for Under the River if you win off that last discard.

Contrast with Under the Sea

• Under the Sea is the one-han yaku for self-drawing the last tile from the wall.
• Under the River is specifically for winning on the last discard by an opponent.

Yaku Value: Under the River is worth one han. It can be combined with any other yaku your hand satisfies.

Rare Occurrence: Hands often end before the final discard—someone wins earlier, or the round ends in a draw. As a result, Under the River naturally happens infrequently.

What is the Strategy and Risk of Under the River?

Push or Fold Decisions: When the round is about to conclude, a player who is in tenpai (one tile away) may push aggressively, hoping the final discarder provides the winning tile. Conversely, a player who suspects someone might be waiting on that final discard might opt for a safer tile, especially if they themselves are not in tenpai.

Combining with Other Yaku: Although Under the River alone only provides one han, you can stack it with yaku such as All Simples, Yakuhai, or even Riichi (if your hand was closed). This can create a surprising last-second swing in points.

Psychological Element: Players often become more cautious with their final discards, knowing the risk of giving away a Under the River win. Watching for “safe” discards near the end can prevent a last-tile upset.