Thirteen orphans 国士無双 · kokushi musou

One of each of the thirteen terminal and honor tiles, plus a duplicate of any one of them.

Count your types at the deal. Kokushi is worth considering when your starting hand holds nine or more of the thirteen terminal and honor types, and it gets comfortable around ten or eleven. The routine from there is mechanical: keep one of each type you have, keep one pair, discard the middle tiles. Those middle-tile discards are also the tell — experienced opponents read a kokushi attempt within a few turns and stop letting honors go.

Tenpai comes in two shapes. Hold twelve types with one of them paired and you wait on the single missing type, four live tiles at most. Hold all thirteen types single and any of them can pair you up — the thirteen-sided wait. That second shape needs a furiten フリテン check: every terminal and honor is now a winning tile, so even one of them in your own discards blocks ron. See how furiten works.

The real cost is that you can't turn back. Hoarded terminals and honors don't reassemble into a normal hand, so treat kokushi as a go-or-fold commitment: push while the type count supports it, and once two or three of the tiles you need are dead in the discards, switch to defense. The consolation is a hand full of honors, which often double as reasonable tiles to fold with.

Key points

• The only standard hand that is neither four-sets-and-a-pair nor seven pairs
• The thirteen-sided wait version (all thirteen tiles single, waiting on any of them) is a double yakuman in many rules
• In many rulesets it may rob even a closed kan (chankan) — the lone exception in the game, though WRC rules do not allow it

Related yaku

• Robbing a kan 搶槓 — Win by taking the tile an opponent adds to an existing pon to upgrade it into a kan.

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