Red 5 Characters Mahjong Tile: Aka uuwan (赤伍萬)

Did you know

Each red five in a winning hand adds 1 han, like a dora, wherever it sits in the hand. It is not a yaku, so it can't win a hand on its own. See aka dora.
If a 4 of characters is the dora indicator, this tile counts twice: once as dora and once as red.
Red fives are a Japanese invention. The red 5 of dots came first, in 1964; reds in the other suits followed. They caught on slowly, through parlor house rules and computer mahjong, and are now the norm.¹²

At the table

It fits in three sequences, the most any tile can.
It is suji to the 2 and 8: once an opponent has discarded and , a two-sided wait on the 5 would leave them furiten, which makes it a safer discard against them.
It is dora when is the dora indicator. Turned up as the indicator itself, it makes dora.

Yaku it can help

Aka Dora each red five adds 1 han
Tanyao simples only
Chinitsu one suit only
Chuuren Poutou the nine gates, all in one suit

Where the characters come from

Mahjong's three suits are older than the game. They come from Chinese money-suited playing cards, whose suits were coins, strings of coins and myriads. A myriad is ten thousand coins, a hundred strings of a hundred, and that is what 萬 means: ten thousand.³²

So a character tile is a sum of money: 三萬 is thirty thousand. The oldest surviving sets, from the 1870s, write the short form 万, as the money cards did; Japanese sets use the full 萬. In Japan the suit is read both manzu and wanzu.⁴⁵