Reiwa Dai Shogi

After taking a bit of a break from inventing chess variants to work on other things, I had an idea to make a variant of Dai Shogi with better piece balancing. After talking with H. G. Muller about it for a while, I eventually decided to make a Dai Shogi variant using only the moves that appeared in that game, called Reiwa Dai Shogi (令和大将棋 reiwa dai shōgi, "Reiwa great chess"). Thanks to the recent invention of Shock Chess, I was able to simplify the Lion-trading rules from Chu to a single rule which was simpler and more effective, which was helped along by the invention of Raichu Shogi. As for the rest of the game, it took a lot of trial and error, but I was successful.

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 pieces are enlarged versions of H. G. Muller's Mnemonic pieces. The Shogi pieces used in the diagram and the Pieces section are my own.

Pieces

All pieces that appear in Chu Shogi are the exact same as in that game (except Lions are not bound by trading rules due to not being the strongest piece in the game). Most of these are quite normal as far as Chess pieces go, with moves that either step or slide along orthogonals and diagonals. (They can slide in some directions, and step in others, though.) Rarely, a piece will be able to jump two squares in a straight line, or even more rarely an oblique jump like that of the Chess Knight.

Note: The non-Chu Shogi pieces in this game usually appear in other historical Shogi variants, but most are given different moves here for balancing reasons.

A few of these pieces have special properties, which are disccussed below:

Lion and Buddhist Spirit

The Lion moves as a King, but up to twice per turn and in independent directions, even if the first King move captures something, or can make these two steps as a jump to any square that is not the starting square. This ability is commonly known as a "Lion move" or "Lion power," and includes all the options that it implies. So the Lion can:

• move or capture by leaping to any square in the 5x5 area surrounding it,
• capture an adjacent piece, and then go on moving or capturing once more as a King,
• move to an adjacent empty square and back, effectively passing a turn.

The Buddhist Spirit moves as a Lion or as a Queen.

Horned Falcon, Soaring Eagle, and Strong Bear

The Horned Falcon, Soaring Eagle, and Strong Bear, only available through promotion, have a limited form of Lion move. They can make up to two steps, continuing after a capture, but only along the same ray. So for the (optional) second step they can only decide if they want to continue in the same direction, or move back to their starting square. Much like the Lion's move, these two steps can also be made as a jump to the second square along the ray. The Horned Falcon, Soaring Eagle, and Strong Bear have such a move only in one, respectively two and three of the eight directions, and slide in all other directions.

Great Shark and Mountain Crane

The Great Shark and Mountain Crane also have linear Lion moves, but are more complicated. They have limited slides of up to two squares in one, respectively two of the eight directions. The Mountain Crane can also slide in the same direction as two of its Lion moves.

Rules

Deciding who moves first

A furigoma (振り駒 piece toss) is used to decide who moves first. One of the players tosses five pawns. If the number of tokins (promoted pawns, と) facing up is higher than unpromoted pawns (歩), then the player who tossed the pawns plays Gote (後手 White) (that is, getting the second move).

The players may also decide who goes first through a game of chance or a mutual agreement.

Object of the Game

The goal is to be the first player to capture all of the opponent's royal pieces. The royal pieces are the King and Prince.

Promotion

The promotion zone is the farthest five ranks of the board (at the original line of the opponent's Pawns and beyond). A piece may promote if it enters the promotion zone (starts outside, ends within), or starts within the promotion zone and captures something. Promotion is done by flipping the piece over, revealing its promoted value. Promotion is optional, with one exception - a piece must promote if it would otherwise have no legal moves on subsequent turns. As such, Pawns, Lances, and Ram's-Head Soldiers must promote on the last rank.

The King, Buddhist Spirit, Lion, and Queen do not promote, nor can already promoted pieces promote further.

Spirit-Trading Rule

If a player captures a Buddhist Spirit (including via hit-and-run capture or double capture) and the capturing piece is not a King or Prince, their opponent is forced to immediately pass their next turn, effectively granting that player an extra turn. Only one forced pass may be granted per turn (that is, capturing multiple Buddhist Spirits in the same turn only grants one extra turn).

Check

There is no rule requiring a player to keep their King and/or Prince out of check. A King or Prince is in check when it could be captured on the opponent's next move. This also extends to situations where forced turn passes from Lion captures allow the opponent to immediately capture the player's King and/or Prince.

There are a couple corollaries to this rule. When the forced turn pass prevents the affected player from resolving a check, that player is immediately checkmated. Conversely, even when in check the player can capture a Lion elsewhere, as freezing the opponent's army is considered to resolve the check. The next move then of course would have to truly resolve it.

A player with both a King and a Prince may sacrifice one of them without losing the game.

Repetition

Repeating a board position with the same player to move is forbidden unless you are in check. In practice, only the fourth repetition is forbidden, to account for human error.

Illegal Move

A player who makes an illegal move loses immediately.

This rule may be relaxed in casual games, where a player can take back the illegal move and make a legal move.

End of the Game

A player wins when they leave their opponent with no royal pieces (King or Prince) on the board. In practice this winning condition is rarely fulfilled, as a player will usually resign when loss is inevitable. There are also other ways a game can end.

Mate

A player is mated if there is no legal move they can make that will leave at least one royal piece (King or Prince) on the board. Mate is an effective win for the player delivering it, regardless of whether the mate has the King is in check (checkmate) or not (stalemate). In practice, a typical game will usually end when this condition is reached.

Resignation

At any time, a player may resign and their opponent wins the game.

Draw

At any time, the players may agree to a draw

In positions where the winning condition is practically impossible to fulfill for either player, the game is considered a draw.

Notes

Implications of the Lion-Trading Rule

The fact that capturing a Buddhist Spirit nets the capturer an extra turn makes it very difficult for the Spirits to disappear from the game. After HSxHS the forced pass prevents recapture, and the capturing Buddhist Spirit will withdraw to safety before your next turn. This makes it unwise to expose the Lions to each other.

Counter-attacking a Buddhist Spirit when your own is attacked also offers no solace - your Spirit will be captured, and the capturing Spirit will withdraw to safety before your next turn.

The only way to successfully trade Buddhist Spirits is if the capturing piece is a King or Prince (though you would still not be very happy if this caused you to be mated afterward!). Without this exception, a King or Prince would simply be able to capture an adjacent attacking Spirit and then withdraw to safety afterward. Thus the Spirit-Trading Rule would facilitate defense, and the exception for the King and Prince repairs that.

Last revised by A. M. DeWitt.