taikyoku shogi

Taikyoku shōgi (Japanese: 大局将棋, lit. "ultimate shogi") is the largest known variant of shogi (Japanese chess). The game was created around the mid-16th century (presumably by priests) and is based on earlier large board shogi games. Before the rediscovery of taikyoku shogi in 1997, tai shogi was believed to be the largest physically playable chess variant ever. It has not been shown that taikyoku shogi was ever widely played. There are only two sets of restored taikyoku shogi pieces and one of them is held at Osaka University of Commerce.^[1] One game may be played over several long sessions and require each player to make over a thousand moves.

Because the game was found only recently after centuries of obscurity, it is difficult to say exactly what all the rules were. Several documents describing the game have been found; however, there are differences between them. It is not too clear how accurate the rules given by modern sources for the game are, because many of the pieces appear in other shogi variants with a consistent move there, but are given different moves in taikyoku shogi. The board, and likewise the pieces, were made much smaller than usual for the other variants, making archeological finds difficult to decipher. Research into this game continues.

It seems that the 'reconstructed' rules were reconstructed by the same people who were caught for spreading rules of a fake 'historical' Cambodian Chess (on 9x9), which they actually cooked up themselves. And they refuse to reveal the sources on which they base this Taikyoku 'reconstruction'.

I, for one, would prefer to believe that pieces with the same name as those known from other Shogi variants should have that same move in Taikyuku Shogi...

BTW, even Tai Shogi (25x25) can hardly be considered 'playable'. The 'Empreror' piece, which you have to capture to win, can teleport to any square (including those occupied by enemies), so it is basically impossible to checkmate it before the opponent is reduced to a bare Emperor. Then you can capture it with your own Emperor. (Which is forbidden while it was protected.) So you have to grind away the hundreds of pieces the players start with in order to finish a game, which can take thousands of moves.