2 han (open)
Honiisou 「混一色」 is a standard yaku. Normally translated as a "half flush", this yaku features a hand composed only of honor tiles and tiles of a single suit. If the hand contains no honor tiles, then the chinitsu yaku is counted instead.
A player's discard pile may lack one particular suit. This may be an indicator of a honitsu hand being developed.
^ Ippatsu requires riichi to be of any use.
Honitsu is aligned to a single suit. Therefore, this yaku is compatible with other yaku, that follows that pattern; and multiple suited yaku do not apply, namely sanshoku and sanshoku doukou. Naturally, the "single suited" yaku of ittsu can merge with honitsu, only if the fourth tile group is of the same suit or is a set of honours. Other yaku are able to function with multiple suits; but they are also possible using single suits, namely toitoi and sanankou. The same applies for chiitoitsu. Commonly, this yaku works with yakuhai, and likewise, shousangen.
Of course, honitsu is not compatible with chinitsu, because every chinitsu hand is honitsu. Honitsu combined with tanyao or junchan would actually imply chinitsu instead, since there would be no honours.
This yaku is affected by kuisagari. The hand value decreases by 1 han when open. Despite that property, honitsu hands can produce value as it is still 2 han when open. Added value can easily be gained with the combination of another yaku or even some dora. In this case, honitsu hands can be conveniently open without significantly losing value.
Bakahon 「バカホン」 is a slang term for a basic honitsu hand with open calls. No other han are scored, either from yaku or dora, meaning that the hand will score low (usually 2000 points).
- Honiisou in Japanese Wikipedia