Yaku guides · 10 / 17
Ittsuu: a pure straight in one suit
Ittsuu combines the 123, 456, and 789 sequences in one suit, for 2 han closed or 1 han when the hand is open.
The principle
Ittsuu (一気通貫) covers all nine numbers of one suit through three separate groups: 123, 456, and 789. It is not a single nine-tile sequence. Each block occupies one normal group slot in the completed hand.
Rule and example
The yaku is worth 2 han closed and 1 han open because of kuisagari. Calling a tile can finish one of the three blocks and speed up the hand, but that speed costs one han and removes the option to declare riichi.
What changes
All three sequences must stay in the same suit. A hand with 123m, 456m, and 789p does not have ittsuu. The yaku can combine with honitsu or chinitsu when the fourth group and pair also respect the selected suit and any honors allowed by the flush.
Mistake to avoid
Ittsuu often appears as a secondary plan around two blocks that already exist. If the third block needs several scarce tiles, keeping a wider ryanmen shape may be stronger. Value the possibility without automatically sacrificing ukeire for it.
Rules references
- Tenhou rulesReference profile used for game mechanics and scoring.
- WRC Rules 2025International rules compared whenever their options differ from Tenhou.