Sannin shogi

[1] The board is thought to have originally been in the shape of an equilateral triangle bordered by three rectangles which contained the players' home territories and promotion zones.

The three players occupy non-adjacent sides of the board; the three ranks nearest to them are their territories and their opponents' promotion zones.

The central cell is called the Pleasure Garden and is an additional promotion zone, except for the king.

The king (K; "public opinion" in Tanigasaki's nomenclature) may step to any adjacent (orthogonal) cell (1, 3, 5, 7, 9, or 11 o'clock).

A promoted king (+K; "rising sun" or "sunlight") may range along any of the twelve orthogonals or diagonals.

A non-allied king (promoted or otherwise) that reaches the central cell of the board (the Pleasure Garden) wins the game.

A promoted bishop (+B; "witchcraft") gains the power to step to any adjacent (orthogonal) cell.

A promoted silver (+S; "treasure") gains the power to range along the forward and rear diagonals (12 and 6 o'clock).

A promoted lance (+L; "transformation") gains the power to range along the rear orthogonals (5 and 7 o'clock) as well.

The restriction against dropping on the far rank (row a in the case of Middle) applies only to pawns and lances, as all other pieces can move from that position.

There are three promotion zones: Both of the opposing player's territories, plus the Pleasure Garden (the central cell of the board).

When using standard game pieces, promotion entails turning the king blank side up.

They may attack each other, but not place each other in check until the third player is defeated, at which point the alliance is annulled–alliances cannot otherwise be broken.

Allies may attack each other to gain pieces-in-hand for drops, or to weaken each other in anticipation of the two-player end game.

However, if two players gang up on the third at any time during the game, subject to the following definitions, an alliance is automatically formed.

Possible gain by the third player elsewhere is disregarded, even if this were to make up for the material loss caused by the coordinated attack.

Likewise, the sequences of the moves are disregarded, even if they prove the loss of material is more apparent than real.

For the purposes of calculating threats of uneven exchange, promoted values are ignored; the ranging pieces rook and bishop are considered equivalent and more valuable than the step movers gold, silver, knight, and the lance, which are in turn considered equivalent and more valuable than a pawn.

Finally, check can be considered the extreme case of uneven exchange, so the value scale is Regardless of whether the situation is a discovered or a dual attack, it does not force an alliance if any attacking move is a direct defense against a threat of material loss, as defined above.

Several rules that change or come into force when an alliance is made have been mentioned above: Here are the first six moves of a game played at a meeting of the International Shogi Research Group on 28 May 1932.

John Fairbairn describes some of the moves as "strange" considering the professional level of the players.

Setup. If the pawns were removed, the rooks could capture the bishops, and the bishops could capture each other, as could the lances.
K = king 玉, G = gold 金, S = silver 銀, L = lance 香, B = bishop 角, R = rook 飛, N = knight 桂, p = pawn 歩.
The ranks are numbered a–m, and the files slanting left 1–13.
The twelve directions of movement, "orthogonal" (blue) vs "diagonal" (green). 駒 represents the moving piece. The promoted rook moves along any of the six solid blue lines, whereas the bishop moves along any of the six discontinuous green lines.
The twelve directions of movement and the corresponding hours on a clock face. The blue cells in the odd-hour directions are the first cells of the six orthogonals; the green cells in the even-hour directions are the nearest cells of the six diagonals. These are the twelve cells that step movers can reach.
Sannin setup with the original piece names.
Summary of the pieces and their promoted movements
The king steps all orthogonal directions; it is not equivalent to the standard shōgi or western king due being unable to move diagonally.
The promoted king ranges all directions; it is equivalent to a western queen with the additional power of "illumination" and status as a royal piece subject to check.
The rook ranges along the 1,3,6,9,11 o'clock directions.
The promoted rook ranges orthogonally; it is equivalent to the standard-shōgi rook.
With the pawns removed at startup, the rooks (white) threaten the opposing bishops (orange) while protecting their own bishop.
The bishop ranges diagonally; it is equivalent to the standard-shōgi bishop.
The promoted bishop ranges diagonally and steps orthogonally; it is equivalent to the standard-shōgi dragon horse
With the pawns removed at startup, the bishops (white) threaten each other. They protect the neighboring gold generals (green).
The gold general steps at 1,3,6,9,11,12 o'clock.
The knight steps at 2,3,4,8,9,10 o'clock.
The silver general steps at 1,2,5,7,10,11 o'clock.
The promoted silver general gains a ranging move at 6 or 12 o'clock.
The lance ranges at 1 or 11 o'clock; it is equivalent to the standard-shōgi lance but with the ability to attack either opposing side.
The promoted lance ranges at 1,5,7,11 o'clock; it acquires the ability to reverse its course.
With the pawns removed at startup, each lance (white) threatens the two neighboring lances. With the rook and bishop out of the way (bottom), they also threaten the rook and bishop across the board (orange), and the two lances behind them.
The pawn steps at 1 or 11 o'clock; it's equivalent to the standard-shōgi pawn but with the ability to attack either opposing side.
The promoted pawn moves as a gold general, as does the standard-shōgi tokin.
Castling and promotion zones. Orange cells are Middle's home territory, where the king may jump when castling. Green cells are Middle's three promotion zones. Tan cells are international territory.