Uradora, literally the under dora, is a supplementary dora available only to a player who wins a hand while declared in riichi. Its indicators lie face-down directly beneath the ordinary dora indicators in the dead wall, hidden until that riichi hand is completed and then flipped over. Each one designates its uradora tiles by the same succession rule as a normal dora indicator.
When a riichi player wins, they reveal as many uradora indicators as there are face-up dora indicators. Every completed kan adds one visible indicator and therefore one potential uradora indicator. In an ordinary hand, each matching tile adds one han; dora are not counted on a genuine yakuman.
Uradora is a bonus, not a yaku. Riichi already supplies the required yaku, but the number of uradora remains unknown until the win. Open hands and damaten have no access to it.