Chiitoitsu

Chiitoitsu

Type	Yaku
Kanji	七対子
English	Seven pairs
Value	2 han (Closed only)
Speed	Medium
Difficulty	Medium

Chiitoitsu 「七対子」, also known as chiitoi or niconico, is a yaku scored when a hand has seven pairs. It is one of the two exceptions of the "four melds and one pair" rule for winning hands, the other being kokushi musou. Because the hand does not use melds, it can only be closed.

Under most rulesets, no two pairs may be identical (certain house rules may allow duplicate pairs, though).

Tile diagram

Winning tile:

Development

Tenpai for chiitoitsu always uses the wait of tanki (pair wait) in order to complete the seventh and last pair for the hand.

Given the number of pairs in this hand, it is often tempting to call pon to turn pairs into triplets. However, toitoi is generally slower if you do not have any ankou (triplets) yet. This is especially true if the hand sits at iishanten for chiitoitsu.

Nevertheless, transitioning to other yaku may be favorable if the hand develops at least one ankou. In this case, players may find themselves looking to develop a toitoi hand, sanankou, or even suuankou. Whatever the case may be, this consideration takes some discretion, particularly when taking into account the number of tiles available, current point standing, and/or number of tile draws remaining.

Also, note that the pairs must be distinct; having four of the same tile does not count as two pairs under standard rulesets. Even in rules that do allow four-of-a-kind to count as two pairs, a call for "kan" would not count, as a kan is treated as a triplet.

Hand interpretation

Unlike most mahjong hands, chiitoitsu is an exception to the "four groups and a pair" pattern. Instead, tiles are groups into pairs or toitsu. As such, the tile groupings cannot be interpreted other ways. For this reason, chiitoitsu is also granted a unique fu count of 25, which remains static.

Shanten

The shanten count for chiitoitsu is simpler to count, which can be marked by the number of pairs in the hand.

Shanten	Pair count	Hand	Comment
Tenpai	6		Obvious choice for chiitoitsu while in tenpai or 1-shanten. The choice of riichi will depend on the waiting tile, current hand, and current score. A 1-shanten hand waits to pair one of three tile types for tenpai. Upon reaching tenpai, one of the three must be discarded.
1	5
2	4		A hand with four pairs may consider chiitoitsu - only one more pair is needed to get to 1-shanten. It can go either way, depending on the rest of the hand (e.g. a hand with many ryanmen + 1 sequence should go for the regular hand structure).
3	3		A hand with three pairs is inefficient either way, unless a pair can easily be ponned. Prefer the regular hand structure, unless a 4th pair is drawn very early.
4	2		Attempting chiitoitsu is unreasonable. It is better off using the regular hand structure.
5	1

Compatibility

Main article: Yaku compatibility

^ Ippatsu requires riichi to be of any use.

RCH

DRI

IPP

SMO

TAN

PFU

IPK

ITT

YAK

SDJ

SDO

TOI

SNA

SNK

CHA

JUN

RPK

SSG

HRO

HON

CHN

CHI

RIN

HAI

HOU

CHK

CHI

The composition of this yaku makes it very restrictive regarding its combination with other yaku. Chiitoitsu cannot be combined with any yaku dependent on tile groups of three, as this yaku consists of only pairs. Chiitoitsu combined with chanta gives honroutou, and it cannot be combined with junchan as there are only six different terminals, but chiitoitsu requires seven distinct pairs.

This yaku forbids kan, so rinshan is incompatible. Chankan is also incompatible. A hand in tenpai for chiitoisu always has a copy of the winning tile, thus making it impossible for other players to make the added kan call required for chankan.

With iipeikou or ryanpeikou

A chiitoitsu hand may collect sequential series of paired tiles, which may look like iipeikou or even ryanpeikou. Both yaku are incompatible with chiitoisu, as once again, all tiles are considered to be in pairs, not sequences.

Value

Main article: Scoring table

As a special exception to scoring, this hand is always given 25 fu. No other fu are awarded: not for yakuhai pairs, tanki waits, or closed ron. It is not rounded up to 30 fu. This produces a distinct set of scoring values:

Position	2 han	3 han	4 han	5 han or more
Non-dealer tsumo Non-dealer ron	Not possible 1600	800/1600 3200	1600/3200 6400	Mangan, Haneman, etc.
Dealer tsumo Dealer ron	Not possible 2400	1600 4800	3200 9600

A 2 han chiitoitsu tsumo is not possible, as chiitoitsu is always closed, so it also scores mentsumo. Like all hands, once you reach 5 han or more, fu is no longer relevant for scoring.

Note that, if the hand is below mangan, chiitoitsu can be thought of as a 1 han 50 fu hand.

• 2 han 25 fu = 1 han 50 fu
• 3 han 25 fu = 2 han 50 fu
• 4 han 25 fu = 3 han 50 fu

High scoring chiitoitsu hands are possible even without dora. The highest possible hand is riichi, ippatsu, tsumo, haitei and chinitsu. With the 2 han for chiitoitsu, the combination brings the hand to a whopping 12 han. Note that tanyao cannot be added, as the hand 22334455667788 can be scored as ryanpeikou for an additional 1 han. In some rule variations, this hand is an optional yakuman, known as "daisharin", "daichikurin", or "daisuurin", depending on the suit.

With dora

Main article: Dora

All tiles in this yaku must be in pairs. Therefore the dora tiles also tend to occur in pairs. The red dora, if used, are exceptions, since they can be paired with non-red versions of the tile.

External links

• 七対子

Chiitoitsu in Japanese Wikipedia