Under the Sea

What is Under the Sea in Japanese Mahjong?

Under the Sea, is a one-han yaku in Japanese Riichi Mahjong. It is awarded to a player who completes their winning hand by drawing the very last tile available in the live wall. While it’s relatively rare and heavily dependent on timing, combining it with other yaku can yield a satisfying and occasionally high-scoring finish to a hand.

How to Achieve Under the Sea？

Last Tile from the Live Wall: There is a finite number of tiles in the “live wall” (the portion of the wall from which players normally draw). When you draw the final tile in the wall—and it completes your hand—you qualify for Under the Sea.

Self-Draw Only: This yaku only applies when you personally draw the last tile. If you win off another player’s discard on the final discard of the game, that is a different one-han yaku called Under the River.

Open or Closed Hand: Under the Sea does not require a fully concealed hand. You can still earn this yaku with an open hand.

Yaku Value: Under the Sea is worth one han, regardless of other circumstances. It adds to any other yaku in your final hand.

What is the Strategy and Risk of Under the Sea?

Rare Opportunity: Because it depends on drawing the absolute last tile of the round, Under the Sea is naturally uncommon. Many rounds end before reaching the final tile (e.g., someone wins earlier, or the wall is exhausted in a draw).

Timing and Luck: There is no guaranteed method to “force” Under the Sea. It is largely situational and reliant on the game’s progression. However, if you see the wall running low, you may choose to push for a quick tenpai if you believe you can survive until the very last draw.

Combined Yaku

Under the Sea can combine with other yaku to increase total han. For example:

• All Simples: If your hand excludes terminals and honors.
• Riichi: If you stayed fully concealed and declared Riichi earlier.
• Fully Concealed Hands: If your hand is concealed and you win by self-draw. Stacking these can turn a typically low-value yaku into a more significant hand.

If you’re close to the last tile in the wall and not in one tile away from winning, you might shift to a purely defensive stance—especially if another player appears to be in a position to claim Under the Sea. Denying them an easy win can preserve your points.