Ikkitsuukan (Pure Straight) - The 1-2-3-4-5-6-7-8-9 Yaku

What is Ikkitsuukan?

Ikkitsuukan (pure straight) is a mahjong yaku that requires 123, 456, and 789 sequences in the same suit, worth 2 han. Often called “Ittsuu” for short, it’s a beautiful yaku that runs straight from 1 to 9.

Closed it’s 2 han; with calls it drops to 1 han (kuisagari). It’s relatively easy to understand and aim for as a beginner.

Conditions

Open vs Closed

*Kuisagari = losing 1 han when calling

Example Hands

Basic Form

Hand: 123m 456m 789m 234p 5s5s
Complete: 1-9 in manzu + another meld + pair

With Calls

Chi: 123m (sideways) 456m (sideways)
Hand: 789m 456p EE

Compatible Yaku

When to Aim for Ittsuu

Starting Hand Assessment

Calling Decisions

1. Early game calls

   • 123 or 789 actively
   • Lock them in early

2. Mid-game calls

   • Chi 456 immediately
   • Prioritize completion

3. Late game calls

   • Even 1 han has value
   • Prioritize winning

Building Strategy

Typical Flow

Starting hand: 5-6 tiles in one suit
↓
Early: Collect 1-3 and 7-9 range
↓
Mid: Complete or chi 456
↓
Late: Ittsuu complete, tenpai

Efficient Approach

1. Prioritize outer sequences

   • Build 123 and 789 first
   • 456 can come later

2. Use chi effectively

   • Call outer sequences
   • Self-draw the 456

3. Stay flexible

   • Keep sanshoku in view
   • Flush hands possible too

Statistics

Occurrence rates:

• Closed: ~1.5%
• With calls: ~2.0%
• Relatively easy 2-han yaku

Compared to Other 2-han

1. Chiitoitsu (~3%)
2. Sanshoku (~2%)
3. Ikkitsuukan (~2%)
4. Toitoi (~1.5%)
5. Chanta (~1%)

Common Mistakes

1. Different suits confusion

   • 123m 456p 789s is invalid
   • Must be same suit

2. Sequence order

   • Don’t need 123→456→789 order
   • Can be scattered in hand

3. Triplet confusion

   • 111, 444, 777 doesn’t work
   • Must be sequences

4. Kuisagari calculation

   • Open: 2→1 han
   • Calculate with other yaku

Historical Background

Name Origin

Meaning of “Ikkitsuukan”:

• “Pass through in one go” from 1 to 9
• Continues without interruption
• Also called “Ittsu Ryuu” (one dragon) in Chinese

Why It’s Popular

1. Understandability

   • Easy for beginners
   • Visually beautiful

2. Practicality

   • Relatively easy to make
   • 2-han value

3. Achievement feeling

   • Fun gathering 1-9
   • Satisfaction on completion

Related Terms

• Shuntsu: Three consecutive tiles
• Kuisagari: Han reduction when calling
• Sanshoku: Compatible yaku
• Chinitsu: Often combines
• Honitsu: Often combines

Summary

Ikkitsuukan (Pure Straight) requires 123, 456, and 789 sequences in one suit for 2 han. Closed is 2 han, open drops to 1 han, but it’s popular as an easy-to-understand yaku. Beginners should remember “same suit 1 through 9” and aim actively when dealt many tiles of one suit. Stay flexible with sanshoku and flush combinations while building your hand.