Pure straight 一気通貫 · ittsuu (ikkitsuukan)

Short answer: Ittsu (pure straight) is a yaku for holding 1-2-3, 4-5-6, and 7-8-9 of one suit as three sequences, worth 2 han closed and 1 han open.

The sequences 1-2-3, 4-5-6, and 7-8-9 in one suit — a straight through the whole suit.

Value	2 han closed · 1 han open
How often	common

Mahjong hand: 1 of circles, 2 of circles, 3 of circles, 4 of circles, 5 of circles, 6 of circles, 7 of circles, 8 of circles, 9 of circles — 6 of characters, 7 of characters, 8 of characters — 5 of bamboo, 5 of bamboo — 1 through 9 of a single suit as three sequences: 123, 456, 789.

Ittsu shows up when one suit dominates your draws and its tiles spread across the whole range instead of clustering. Hold 12356789p and you are one tile, the 4p, from the full straight. The check that matters: the blocks must sit exactly at 123, 456, and 789, so read your long suit in those frames before you commit to it.

The near-miss is the classic trap. A stretch like 2-3-4-5-6-7 looks close but counts as two ordinary sequences, not as straight blocks, and no single draw repairs it cheaply. The tile that rescues an ittsu hand is often a terminal, the 1 or 9 you were tempted to discard early, so when one suit runs long in your hand, hold its end tiles a few extra turns.

Open, ittsu keeps a yaku but drops to 1 han, which matters mostly as a component: an open straight inside a one-suit hand stacks with honitsu, and if the honors fall away the same shape flows toward chinitsu. Closed, declare riichi and treat the straight as the hand's backbone rather than the whole plan.

Key points

The three sequences must be exactly 123 / 456 / 789 in the same suit — 234, 567 do not count
2 han closed, 1 han open
Natural stepping stone toward honitsu or chinitsu when your hand leans into one suit

Worked example

Mahjong hand: 1 of circles, 2 of circles, 3 of circles — 4 of circles, 5 of circles, 6 of circles — 7 of circles, 8 of circles — 3 of characters, 4 of characters, 5 of characters — 9 of bamboo, 9 of bamboo, winning tile: 9 of circles — 123p, 456p, and 78p, with 345m and a 99s pair. This hand wins on 3p, 6p, or 9p — only the 9p completes the straight.

The 78p block is open on both ends, so the obvious waits are 6p and 9p (the 3p also completes the hand by re-reading the pins). The 9p makes 789p and the full 1-to-9 run. The 6p makes 678p instead — a finished hand, but the 7-8-9 block is missing, so no ittsu.

The price difference is real. Won by ron on the 9p without riichi: ittsu 2 + pinfu 1 = 3 han 30 fu, 3,900 for a non-dealer win. On the 6p it is pinfu alone, 1,000 points. Same wait, same turn — the tile decides.

Common mistakes

Accepting 234-567-89 or other offsets. The blocks must sit exactly at 123, 456, and 789.
Mixing suits. 123m, 456p, 789s is not ittsu (that mixed-suit pattern is not a standard yaku).
Discarding the 1 or 9 too early. In a long suit, the terminal is often the tile that finishes the straight — and when one suit dominates, the hand can grow into honitsu or chinitsu.

Related yaku

Full flush 清一色 — The entire hand is one suit — the highest-value regular yaku in the game.
Half flush 混一色 — The whole hand uses a single suit plus honor tiles.

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