Taikyoku 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 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. 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. Many of the pieces appear in other shogi variants but their moves may be different. The board, and likewise the pieces, were made much smaller, making archeological finds difficult to decipher. Research into this game continues for historical and cultural reasons, but also to satisfy the curious and those who wish to play what could be the most challenging chess-like game ever made. More research must be done however. This article focuses on one likely set of rules that can make the game playable in modern times but is by no means canon. These rules may change as more discoveries are made and secrets of the game unlocked.
Further, because of the terse and often incomplete wording of the historical sources for the large shogi variants, except for chu shogi and to a lesser extent dai shogi (which were at some points of time the most prestigious forms of shogi being played), the historical rules of taikyoku shogi are not clear. Different sources often differ significantly in the moves attributed to the pieces, and the degree of contradiction (summarised below with the listing of most known alternative moves) is such that it is likely impossible to reconstruct the "true historical rules" with any degree of certainty, if there ever was such a thing. It is not clear if the game was ever played much historically, as there is no record of any sets having been made.
Rules of the game.
Taikyoku shogi is very different from other large-board shogi variants: tenjiku shogi, dai dai shogi, maka dai dai shogi, and tai shogi. The most notable differences lie with the piece movements and their promotions.
Objective.
The objective of the game is to capture the opponent's king(s) and prince(s). When the last of these is captured, the game ends. There are no rules for check or checkmate; however, in practice a player resigns when checkmated. Unlike standard shogi, pieces may not be dropped back into play after being captured.
Game equipment.
Two players, Black and White (or 先手 "sente" and 後手 "gote"), play on a board ruled into a grid of 36 "ranks" (rows) by 36 "files" (columns) with a total of 1,296 squares. The squares are differentiated by marking or color.
All players have 804 and Each player has a set of 402 wedge-shaped pieces of 209 types. The players must remember 253 sets of moves. The pieces are of slightly different sizes with the larger pieces near the king and becoming progressively smaller for pieces further from the king, regardless of power. In general, the stronger pieces are nearer to the king.
Several of the English names were chosen to correspond to rough equivalents in Western chess, rather than as translations of the Japanese names.
Each piece has its name in the form of two or three kanji written on its face. On the reverse side of some pieces are two or three other characters, often in a different color (commonly red instead of black); this reverse side is used to indicate that the piece has been promoted during play. The pieces of the two sides do not differ in color, but instead each piece is shaped like a wedge, and faces forward, toward the opposing side. This shows who controls the piece during play.
Listed below are the pieces of the game and, if they promote, which pieces they promote to; starting with the first row.
Setup.
Below is a diagram showing the setup of one player's pieces. The way one player sees their own pieces is the same way the opposing player will see their pieces.
Game play.
The players alternate making a move, with Black moving first. (The traditional terms 'black' and 'white' are used to differentiate the sides during discussion of the game, but are no longer literally descriptive.) A move consists of moving a single piece on the board and potentially "promoting" that piece or displacing ("capturing") an opposing piece.
Movement and capture.
Most pieces in the game move in a unique manner. An opposing piece is captured by "displacement": That is, if a piece moves to a square occupied by an opposing piece, the opposing piece is displaced and removed from the board. A piece cannot move to a square occupied by a friendly piece (meaning another piece controlled by the moving player).
Each piece on the game moves in a characteristic pattern. Pieces move either "orthogonally" (that is, forward, backward, left, or right, in the direction of one of the arms of a plus sign, +), or "diagonally" (in the direction of one of the arms of a multiplication sign, ×). The lion, lion hawk and knight are exceptions at the beginning of the game, in that they do not move, or are not required to move, in a straight line. (The Buddhist spirit, teaching king, heavenly horse and furious fiend are similar, but they only appear as pieces promote.)
Categories of movement.
Many pieces are capable of several kinds of movement, with the type of movement most often depending on the direction in which they move. The movement categories are:
Step movers.
Some pieces move only one square at a time. (If a friendly piece occupies an adjacent square, the moving piece may not move in that direction; if an opposing piece is there, it may be displaced and captured.)
The step movers are the prince, generals (except: bishop, rook, pig, vice, great and wood), wolves, earth dragon, running horse, running rabbit, turtle snake, turtle dove, flying swallow, rain dragon, mountain stag, running pup, running serpent, side serpent, yaksha, Buddhist devil, violent stag, drunken elephant, neighboring king, chariots (except: reverse, running and copper), right tiger, left tiger, wind dragon, free pup, rushing bird, old kite, bears (except running), side boar, cloud eagle, flying cat, little standard, cloud dragon, soldiers (except soldier and chariot), violent ox, dark spirit, deva, howling dog, side mover, prancing stag, ferocious leopard, fierce eagle, poisonous snake, flying goose, strutting crow, blind dog, Chinese cock, phoenix, kirin, side ox, angry boar, liberated horse, flying cock, monkeys, barbarians, vermillion sparrow, swooping owl, old rat, cat sword, swallow's wings, blind tiger, side flyer, coiled serpent, reclining dragon, go between, dog, vertical mover, vertical pup, vertical horse, dragon horse, dragon king and pawn.
Limited ranging pieces.
Some pieces can move along a limited number (2 to 7) of free (empty) squares along a straight line in certain directions. Other than the limited distance, they move like ranging pieces (see below).
The limited ranging pieces are the king, standards, free dream-eater, wooden dove, dragons (except: rain, side, wind, cloud, flying and reclining), demons, beast cadet, mountain eagle, white tiger, ceramic dove, turtle dove, captive officer, mountain stag, side serpent, great dove, running tiger, running bear, yaksha, Buddhist devil, guardian of the Gods, wrestler, gold chariot, running stag, beast officer, free pup, rushing bird, old kite, peacock, phoenix master, kirin master, silver chariot, vertical bear, pig general, chicken general, horse general, ox general, silver rabbit, golden deer, captive cadet, great stag, stone chariot, cloud eagle, mountain falcon, vertical tiger, copper chariot, golden bird, prancing stag, water buffalo, fierce eagle, water general, mountain general, fire general, turtles, vertical wolf, donkey, enchanted badger, flying horse, angry boar, violent bear, liberated horse, barbarians, center master, roc master, horseman, soldiers (except: rook, ram's-head, spear and sword), wing general, wind general, wood general, great master and roaring dog.
Jumping pieces.
Several pieces can "jump", that is, they can pass over any intervening piece, whether friend or foe, with no effect on either.
The jumping pieces are the wooden dove, running horse, mountain eagle, phoenix master, kirin master, knight, lion, great stag, vice general, flying cat, mountain falcon, golden bird, flying dragon, phoenix, kirin, turtles, treacherous fox, center master, roc master, free eagle, lion hawk, great master, horned falcon, soaring eagle, roaring dog and lion dog.
Ranging pieces.
Many pieces can move any number of empty squares along a straight line, limited only by the edge of the board. If an opposing piece intervenes, it may be captured by moving to that square and removing it from the board. A ranging piece must stop where it captures, and cannot bypass a piece that is in its way. If a friendly piece intervenes, the moving piece is limited to a distance that stops short of the intervening piece; if the friendly piece is adjacent, it cannot move in that direction at all.
The ranging pieces are the standards, queen, free dream-eater, wooden dove, dragons (except: violent, flying and reclining), demons, running horse, mountain eagle, whale, running rabbit, tigers (except blind), turtle snake, ceramic dove, lance, oxcart, chariots, flying swallow, running pup, running serpent, great dove, running bear, running stag, running wolf, free pup, phoenix master, kirin master, vertical bear, side boar, silver rabbit, golden deer, great stag, cloud eagle, bishop, rook, side wolf, mountain falcon, soldiers (except: sword, burning and cross-bow), violent ox, golden bird, white horse, howling dog, side mover, water buffalo, turtles, vertical wolf, side ox, liberated horse, treacherous fox, roc master, vermillion sparrow, horseman, swallow's wings, side flyer, great master, side monkey, vertical mover, flying ox, vertical pup, vertical horse, dragon horse, dragon king, horned falcon, soaring eagle, roaring dog and lion dog.
Hook moves (changing tack).
The hook mover, long-nosed goblin, Capricorn, and peacock can move any number of squares along a straight line, as a normal ranging piece, but may also abruptly change tack left or right by 90° at any one place along the route, and then continue as a ranging piece. Turning a corner like this is optional.
The range covered by a hook move is the equivalent of two moves by a rook, or two moves by a bishop, depending on the piece. However, a hook move is functionally a single move: The piece cannot capture twice in one move, nor may it capture and then move on. It must stop before an intervening piece (unless it first changes direction to avoid it), and must stop when it captures, just like any other ranging piece. It can only change direction once per move.
Area movers.
The lion and lion hawk may take "multiple" (2) steps in a single turn. These do not have to be in a line, so these pieces can potentially reach every square within two or three steps of the starting square, not just squares along one of the diagonals or orthogonals. Such moves are also useful to get around obstructions. An area mover must stop where it captures.
Limited range jumping pieces.
The golden bird and several promoted pieces have the option of jumping a limited number of squares, and then continuing on in the same direction as a ranging piece.
Range jumping (flying) pieces.
The ancient dragon may jump over any number of pieces, friend or foe, along a straight line, but only when making a capture. Otherwise it moves as a ranging piece.
Range capturing pieces.
The great general, vice general, rook general, bishop general, violent dragon and flying crocodile may jump over any number of pieces, friend or foe, along a diagonal or orthogonal. They capture "all" pieces they jump.
However, they may only jump pieces of "lower rank", whether friend or foe. The relevant ranking is:
Individual pieces.
Stone general (石将).
"Because it cannot move orthogonally or backward, a stone general can only reach less than half the squares on the board. "
Cat sword (猫刄).
"Because it cannot move orthogonally, a cat sword can only reach half the squares on the board. "
Old kite (古鵄).
Kite here refers to the bird of prey.
Captive cadet (禽曹).
"When it promotes to a captive officer (see above), it demotes (moving only two squares orthogonally instead of three)."
Bishop ().
"Because it cannot move orthogonally, a bishop can only reach half the squares on the board."
Divine sparrow ().
"Note : this description is ambiguous and can be interpreted two ways."
Fire demon ().
"It cannot burn other pieces as in tenjiku shogi."
Earth dragon ().
The Japanese Wikipedia describes another set of movements for this piece.
Free demon ().
The Japanese Wikipedia describes another set of movements for this piece.
Long-nosed goblin (tengu) ().
"Unlike in other shogi variants, in taikyoku the tengu cannot move orthogonally, and therefore can only reach half of the squares on the board. This is the move of the capricorn, and may be an error."