Tanyao 「断么九」 or 「断幺九」 is a yaku, consisting of tile groups using numbered tiles 2-8 from any of the three main suits. Any tile numbered 2-8 are classed as chunchanhai 「中張牌」, or simples. Conversely, this yaku must lack the terminal tiles (1 and 9) as well as any honor tiles. Among the yaku, this is one of the more easier to attain; and it is also a cheap yaku. In addition, this yaku may be subject to rule variation of allowing or disallowing its count when opened.
Kuitan 「喰い断」 is a rule allowing open tanyao. If kuitan is disallowed, then it would be specified as "kuitan nashi", and tanyao would be restricted as a closed only yaku. Tanyao takes special interest, due to the ease of its viability. This ease is due to overall number of available tanyaochuu, or simples tiles numbered 2 through 8. The disabling of the rule then discourages players from over relying on opening tanyao hands, especially when not accompanied by other yaku or dora.
Tiles numbers 2-8 are designated as "simples". Its converse, the 1 and 9 tiles plus honor tiles, is grouped as the terminals and honors. So, in order to form a hand with tanyao, players simply discard the terminal and honor tiles and form tile groups with the 2-8 numbered tiles. Given the range of the simple tiles, the number of tiles available to form this yaku is a wide range. This availability makes this yaku a particularly fast one to develop. It is even faster, when used in open fashion. Although, some rules may vary, which disallows the use of tanyao for open hands.
While the hand looks to keep the simples, the discards are composed of the converse: terminal and honor tiles. Sometimes, the simples will be discarded, only because they are not needed to form tile groups.
Like any hand, a tanyao hand can be amplified with dora. Tanyao with dora is particularly used due to both the combined ease and speed of hand development. If the dora are closed within the hand, then there is the added deceptiveness of a cheap hand, that is in reality not the case.
Naturally, tanyao is compatible with any yaku that does not utilize yaochuuhai, which are the terminals (1's and 9's) or honor tiles. The six yaku incompatible with tanyao all require such tiles in some way or another.
As a language short cut, any closed riichi, tanyao, pinfu hand is referred as mentanpin 「メンタンピン」: "Men" for the menzen (closed, and by extension, in a riichi state, not to be confused with menzen tsumo); "tan" for tanyao; and "pin" for pinfu. If the hand wins by discard, then it is simply tanpin 「タンピン」.
With chinitsu and ryanpeikou
- Pinzu (circles), dai sharin – 「大車輪」 or big wheels
- Souzu (bamboo), dai chikurin – 「大竹林」 or bamboo forest
- Manzu (characters), dai suurin – 「大数隣」 or numerous neighbours
These yakuman are awarded for having 22334455667788 in the same suit. This requires chinitsu and ryanpeikou, although this is not enough, as the hand 22334444556677 would qualify for tanyao, chinitsu, and ryanpeikou, but not for one of these yakuman.
The speed of the hand's development justifies the value of the hand at 1-han. This speedy play is associated with cheap value. However, if red fives and other dora are incorporated, then a simple tanyao hand can easily become a very high-scoring one.
- Tanyao in Japanese Wikipedia