Shosu Shogi

Shosu Shogi (小数将棋 shōsū shōgi, "decimal shogi") is a game I invented during my early inventing spree back in 2016 after stumbling upon a Wikipedia article on Okisaki Shogi. It is very similar to standard Shogi, but is played on a 10x10 board. Among the novelties in Shosu Shogi are the Queens, which have the combined powers of the Rook and Bishop, and Gold Generals with the ability to promote. In addition to this, the Lance and Knight have more powerful promoted forms than they do in standard Shogi.

Setup

An interactive diagram has been provided (The Javascript source code was written by H. G. Muller) to make it easier to understand how each piece moves. The Mnemonic piece directory uses H. G. Muller's Mnemonic pieces. The white Shogi pieces used in the diagram and the table in the Pieces section are my own pieces, made using a free online pixel art drawing tool called Pixilart. The tan Shogi pieces are from the Tenjiku Shogi Pieces set. They were made by an unknown author.

Only the location of the pieces of one side are mentioned below. The setup for the other side can be obtained by rotating the board 180 degrees.

First Rank

• Lances (10j, 1j)
• Knights (9j, 2j)
• Silver Generals (8j, 3j)
• Gold Generals (7j, 4j)
• Queen (6j)
• King (5j)

Second Rank

• Bishop (9i)
• Rook (2i)

Third Rank

• Pawns (10h, 9h, 8h, 7h, 6h, 5h, 4h, 3h, 2h, 1h)

Pieces

The following table shows the moves of the pieces. XBetza notation is included for easier reference.

Piece		Promoted Piece
King	The King moves one space in any direction, but not into check. (K)	The King does not promote.
Queen	The Queen moves as it does in Chess - it slides orthogonally or diagonally. (Q)	The Queen does not promote.
Rook	The Rook moves as it does in Chess - it slides orthogonally. (R)	Dragon King	The Dragon King moves as it does in Shogi - it can move as a Rook or as a King. (RF)
Bishop	The Bishop moves as it does in Chess - it slides diagonally. (B)	Dragon Horse	The Dragon Horse moves as it does in Shogi - it can move as a Bishop or as a King. (BW)
Gold General	The Gold General moves as it does in Shogi - it moves one square orthogonally or diagonally forward. (WfF)	Drunk Elephant	The Drunk Elephant moves one square diagonally, sideways, or directly forward. (FfsW)
Silver General	The Silver General moves as it does in Shogi - it moves one square diagonally or directly forward. (FfW)	Gold General	The Gold General moves as it does in Shogi - it moves one square orthogonally or diagonally forward. (WfF)
Knight	The Knight moves as it does in Shogi - it jumps two squares forward and one square sideways. (fN)	Jumping Horse	The Jumping Horse moves like the Knight in Chess - it jumps two squares vertically and one square sideways, or two squares sideways and one square vertically. (N)
Lance	The Lance slides directly forward. (fR)	Vertical Mover	The Vertical Mover can slide vertically or move one square sideways. (WvR)
Pawn	The Pawn moves as it does in Shogi - one square orthogonally forward. (fW)	Tokin	The Tokin moves as it does in Shogi - it moves one square orthogonally or diagonally forward. (WfF)

Rules

Promotion

When a piece moves to, from, or within the owner’s promotion zone, the owner may promote that piece. The promotion zone is the last three ranks of the board - the three ranks occupied by the opponent’s pieces at the start of the game. Promotion is optional – a player need not promote a piece immediately upon entering the promotion zone. However, a piece must promote if it would otherwise have no legal moves left on a subsequent turn. The promotions for each piece are as follows.

Rook => Dragon King

Bishop => Dragon Horse

Gold General => Drunk Elephant

Silver General => Gold General (promoted Silver General)

Knight => Jumping Horse

Lance => Vertical Mover

Pawn => Tokin

A promoted piece that get captured reverts to its unpromoted state. Otherwise, a promotion is permanent. Promoted pieces cannot be demoted in any other way. Pieces can only promote once – promoted pieces cannot promote any further. The King and Queen do not promote.

Lances, Knights, and Pawns

If a Lance, Knight, or Pawn reaches the last rank, it must promote because it would otherwise have no legal moves left on a subsequent turn. A Knight that reaches the penultimate rank must promote for the exact same reason.

Drops

Captured pieces get retained in hand and can be brought back into play under the capturing player’s control. On any turn, instead of moving a piece on the board, a player may return a captured piece to any empty square on the board. This is called dropping the piece, or simply a drop. A drop counts as a complete move. The rules regarding drops are as follows.

• A piece may not be dropped onto an occupied space.
• Pieces that are dropped within the promotion zone do not promote immediately.
• A piece may not be dropped onto a space where it would have no legal moves left on a subsequent turn.

Captures and promotions may occur normally on a subsequent move of the piece.

Lances, Knights, and Pawns

Lances, Knights, and Pawns may not be dropped onto the last rank, as they would have no legal moves left. Knights may not be dropped onto the penultimate rank for the exact same reason.

Pawn Restrictions

In addition to the rules mentioned above, there are special rules concerning pawn drops.

• Two Pawns (Japanese: 二歩 nifu): A Pawn cannot be dropped on a file that already contains an unpromoted Pawn belonging to the same player (promoted pawns do not count).
• Drop Pawn Mate (Japanese: 打ち歩詰め uchifudzume): A Pawn cannot be dropped to give immediate checkmate (although other pieces may be dropped to give immediate checkmate). A Pawn may, however, be dropped to give immediate check as long as it is not also checkmate. A Pawn may also be dropped to give immediate stalemate. This rule does not apply to Pawns that are already on the board.

Check, Checkmate, and Stalemate

When a King is threatened with capture on the next turn, it is in check. A King that is in check must immediately get out of check. This can be done in one of three ways, depending on the situation:

• Moving the King to a safe square
• Blocking the check
• Capturing the attacking piece

If the king is in check and cannot escape capture, it is in checkmate. Checkmate counts as a loss for the checkmated player. If a player's king is not in check but has no legal moves, it is in stalemate. The result of a stalemate is the same as that of checkmate – it is a loss for the stalemated player.

Illegal Move

A player who makes an illegal move loses immediately. Illegal moves include:

• Violating the Two Pawns (nifu) restriction
• Violating the Drop Pawn Mate (uchifuzume) restriction
• Dropping or moving a piece to position where it cannot move
• Making more than one move per turn
• Moving one's king into check
• Moving a piece contrary to how its movements are defined

Repetition Draw 千日手 sennichite - If the same game position occurs four times with the same player to move and the same pieces in hand for each player, then the game ends in a draw.

Impasse - If both kings have advanced into their respective promotion zones and neither player can hope to mate the other or to gain any further material, the players may agree to a draw.

Notes

Similar Games

• Cannon Shosu Shogi
• Futashikana Shogi

Computer Play

You can Play Shosu Shogi online with Game Courier.

Last revised by A. M. DeWitt.