Pure Double Sequence

What is Pure Double Sequence in Japanese Mahjong?

Pure Double Sequence is a one-han yaku in Japanese Riichi Mahjong. It rewards having two identical sequences in a fully concealed hand. Pure Double Sequence is a one-han yaku that requires a fully concealed hand containing two identical sequences in the same suit. While it may not be the highest-paying yaku on its own, it frequently combines with other concealed-hand yaku—like Riichi, Fully Concealed Hands, and Pinfu—to increase the overall hand value. Mastering Pure Double Sequence is a key step toward improving both hand efficiency and scoring potential in Japanese Riichi Mahjong.

How to Achieve Pure Double Sequence?

Two Identical Sequences: You must form a pair of identical runs (e.g., 2-3-4 of dots and another 2-3-4 of dots). Both sequences have to be in the same suit (pin, sou, or man).

Concealed Hand Only: Pure Double Sequence can only be claimed if your entire hand is concealed (no open melds). A concealed kong does not break your closed hand status in principle, but forming a kong might make it more difficult to keep or confirm identical sequences.

Value: Worth 1 han on its own. Cannot be declared if the hand is opened, meaning it’s exclusively a fully concealed yaku.

What is the Strategy and Risk of Pure Double Sequence?

Building the Double Sequence: Naturally occurs when you have, for instance, both 1-2-3 of pin and another 1-2-3 of pin. Because you need the same run twice, it tends to happen more organically if you focus on building sequences in one suit.

Efficiency vs. Chance: Going for Pure Double Sequence shouldn’t drastically slow down your hand, as you’re still collecting sequences that might align well with Pinfu or All Simples if the tiles fit. However, it does rely on drawing very specific tiles twice, so there’s some element of luck.

Combining with Other Yaku: Since the hand must remain concealed, Pure Double Sequence often pairs well with:

• Riichi for an extra one han.
• Fully Concealed Hands if you win by self-draw, for another one han.
• Pinfu if your pair is non-scoring and your waits are two-sided.

Distinguishing from Twice Pure Double Sequence

• Twice Pure Double Sequence is a separate, higher-value yaku (3 han) achieved if you have two distinct pairs of identical sequences.
• If you only have one pair of identical sequences, that’s Pure Double Sequence.

Concealment is Key: Be cautious about calling tiles (chow/pung). Once you open your hand, you forfeit Iipeikou. Prioritize drawing tiles yourself or using closed kan if it aligns with your strategy.

Synergy with Pinfu: Many Iipeikou hands naturally fit the structure of Pinfu (four runs plus a valueless pair), which can yield at least two han when combined.

Defensive vs. Offensive Play: If you’re close to completing Iipeikou, you might decide to pass on a meld that could speed up your hand but reduce its final value. Balancing speed and hand value is a core strategic challenge.

Watch Out for Twice Pure Double Sequence: Sometimes, you can upgrade from Pure Double Sequence to Twice Pure Double Sequence if you happen to draw two separate pairs of identical sequences. Keep your eye on that possibility for a higher-scoring hand.