|English||Two sets of identical sequences|
|Value||3 han (closed only)|
Ryanpeikou is incompatible with other yaku that place conflicting requirements on the mentsu in the hand. Ittsu, sanshoku, sanshoku doukou, toitoi, sanankou, sankantsu, and shousangen are excluded as they are require either three different sequences or at least one triplet/quadruplet. Rinshan kaihou also requires a kan, so it is excluded. Chankan is incompatible because the winning tile must be unique in the winning hand---all four copies of it having been used in another player's kan. Finally, iipeikou is incompatible because it is superseded by ryanpeikou.
This yaku does not combine with chiitoitsu. By definition, chiitoitsu is formed by the collection of seven distinct pairs. In most instances of ryanpeikou, the hands look like chiitoitsu hands. However, ryanpeikou is actually composed of sequences, rather than as independent pairs. The pattern appears as a collection of pairs, when they are actually not. Because of this interpretation, the two yaku remain distinct and incompatible; and it is doubtful, that any house rule allows the combination of the two yaku.
Note that not all instances of ryanpeikou look like chiitoitsu. The following, for instance, is a valid ryanpeikou hand:
Closed only, ryanpeikou is always at 3 han. So, there is no need to be concerned about a lesser value of the hand while open, or kuisagari. The cheapest ryanpeikou hand uses either a kanchan / penchan / tanki wait, or a ryanmen wait with valued honor as the pair. In both cases, the hand produces a 3-han and 40-fu value by ron. By tsumo, it is 4-han and 30-fu.
- Ryanpeikou in Japanese Wikipedia