Toitsu

Toitsu 「対子」, meaning pairs, are a set of two identical tiles. Every hand, including kokushi musou, requires at least one pair to win. Pairs can also be turned into triplets if a third tile is obtained.

Fu

Main article: Scoring

Having a pair of yakuhai tiles is worth fu.

• A pair of normal yakuhai (dragons, seat wind, round wind) is worth 2 fu
• A pair of double yakuhai (wind that is both round and seat wind) is worth either 2 fu or 4 fu, depending on the ruleset.

Chiitoitsu

Main article: Chiitoitsu

Chiitoitsu, literally "seven pairs", i

One yaku is specifically defined as a collection of pairs. Chiitoitsu is directly translated as "seven pairs".