Objective

The objective of the game is to capture your opponent's white whale.

Game equipment

Two players, Black and White (or 先手 sente and 後手 gote), play on a board ruled into a grid of 6 ranks (rows) by 6 files (columns). The squares are undifferentiated by marking or color.

Each player has a set of 12 wedge-shaped pieces, of slightly different sizes. From largest to smallest (most to least powerful) they are:

• 1 white whale (W)
• 1 porpoise (P)
• 1 humpback (H)
• 1 gray whale (G)
• 1 narwhal (N)
• 1 blue whale (B)
• 6 dolphins (D)

Each piece has its initial written on its face. On the reverse side of the porpoise is another letter (K for 'killer whale'), often in a different color (commonly red instead of black); this reverse side is turned up 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.

Because this is a Western shogi variant, and kanji for the whales are difficult even for the Japanese, the pieces use Latin letters rather than kanji.

Setup

This is the starting setup of a game of whale shogi, from the perspective of Black.

Each side places his pieces in the positions shown below, pointing toward the opponent.

• In the rank nearest the player:
  • The white whale is placed just left of center.
  • The porpoise is placed in the adjacent file to the right of the white whale.
  • The humpback is placed in the left corner.
  • The gray whale is placed between the white whale and the humpback.
  • The narwhal is placed adjacent to the porpoise.
  • The blue whale is placed adjacent to the narwhal in the right corner.

That is, the first rank is:

• In the second rank, the six dolphins are placed one in each file.

Gameplay

The players alternate turns, with Black moving first. (The traditional terms 'Black' and 'White' are used to differentiate the sides during discussion of the game, but are not literally descriptive.) A move consists of moving a single piece on the board, displacing (capturing) an opposing piece, or dropping a previously captured piece onto an empty square of the board. Each of these options is detailed below.

Movement and capture

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, ×).

Some pieces are capable of more than one kind of movement, with the type of movement most often depending on the direction in which they move. The movement categories are:

Drops

Captured pieces are truly captured in whale shogi. They are retained "in hand", and can be brought back into play under the capturing player's control. On any turn, instead of moving a piece across the board, a player can take a piece he has previously captured and place it on any empty square, facing the opponent. The piece is now part of the forces controlled by that player. This is termed dropping the piece, or just a drop.

A drop cannot capture a piece; that requires an additional move.

A porpoise cannot be dropped as such. When captured, the porpoise promotes to a killer whale and can only be dropped as a killer whale.

There are three restrictions when dropping dolphins:

• A dolphin may not be dropped on the furthest rank, even though it has a legal move on subsequent turns.
• A dolphin cannot be dropped into the same file (vertical column) as two other dolphins controlled by the same player. For this reason, one may sacrifice a dolphin in order to gain flexibility for drops.
• A dolphin cannot be dropped if the opponent would have no way to prevent his white whale being captured on the next move. In other words, a dolphin cannot be dropped to give immediate mate.

Check and mate

When a player makes a move such that the opponent's white whale could be captured on the following move, the move is said to give check to the white whale; the white whale is said to be in check. If a player's white whale is in check and no legal move by that player will get the white whale out of check, the checking move is also mate, and effectively wins the game.

A player is not allowed to give perpetual check.

Game end

A player who captures the opponent's white whale wins the game. In practice this rarely happens, as a player will resign when checkmated, as otherwise when loss is inevitable.

A player who makes an illegal move loses immediately. (This rule may be relaxed in casual games.)

Another possible (but fairly uncommon) way for a game to end is repetition (千日手 sennichite).

If the same position occurs four times with the same player to play, then the game is no contest. Recall, however, the prohibition against perpetual check. For two positions to be considered the same, the pieces in hand must be the same, as well as the position on the board.

Games which are no contest are usually counted as draws in amateur tournaments, but if a professional-style tournament is to be played the rules may require the game to be replayed with colors reversed (possibly with reduced time limits).

Setup