6 han (closed)
5 han (open)
Chiniisou 「清一色」 is a standard yaku. This yaku is composed of tiles in one suit only. Chinitsu is worth 6 han, but it decreases to 5 han when opened. This yaku is usually referred to as chinitsu or, occasionally, chinichi.
As defined, this yaku is formed by collecting tiles of one suit. Therefore, tiles not of a particular suit are regularly discarded. As a consequence, a player aiming for a chinitsu may be very easily detected via discards alone.
Complex wait patterns
Chinitsu is notorious for developing complex wait patterns. This is due to the homogenous nature of the yaku. The number of potential waiting tiles may range from one tile of the suit to all nine tiles. Strings of consecutive numbers enable this complexity. Without the help of computers, this complexity increases the difficulty in determining the winning tiles upon tenpai.
Chinitsu requires a single suit, so that deems this yaku incompatible with other yaku that demand other tile types. That includes yakuhai, shousangen, as well as sanshoku and sanshoku doukou. Since chinitsu implies honitsu, the latter is not counted together. If combined with chanta, the hand is actually junchan, so that yaku is counted instead. Finally, chinitsu and honroutou would require a hand containing at most eight tiles (the 1s and 9s of one suit), which is impossible.
Due to the relatively high value of this yaku, chinitsu may be involved in the formation of kazoe yakuman. Especially when closed, the 6-han is enough to be almost half necessary to acquire 13-han. Naturally, other yaku and/or dora will have to compose the rest. Though, one particular pattern may form as the yakuman, chuuren poutou.
As a standalone yaku, chinitsu is at least a mangan, even when open. To regain the lost han as an open hand, it simply takes just one dora, or a combination with another yaku, just to bring the hand up to its closed value of a haneman.
- Chiniisou in Japanese Wikipedia
- Game designed with sou tiles only to train reading chinitsu hands.