Rules

Fuseki Shogi starts from a bare board: the players build their own opening position first. Once the 40 placements are done it is ordinary shogi. Balance Shogi adds a short procedure at the very start that weighs the first-move advantage against king safety.

How a game runs

Fuseki Shogi

1. The board starts empty. Starting with Sente, the players alternately place their 20 pieces (9 pawns, 2 lances, 2 knights, 2 silvers, 2 golds, 1 bishop, 1 rook, 1 king) within their own first four ranks, one per turn.
2. Until both players have placed all 20 pieces (40 moves), nothing moves. Only placements.
3. To avoid a double pawn (nifu), filling all four squares of a file with your own non-pawn pieces is illegal.
4. From move 41 it is ordinary shogi. Sente moves first. Checkmate wins.

The 20 pieces

The same 20 pieces as the ordinary opening position, placed by you. The king is one of them and may go down at any time.

• ×9
• ×2
• ×2
• ×2
• ×2
• ×1
• ×1
• ×1
• 20each

Where you may place

The nifu-avoidance rule

There are nine pawns and, as in ordinary shogi, two pawns may not share a file — so the nine pawns end up on nine different files. Fill a file with other pieces and no pawn can go there, which forces a double pawn somewhere else. The rule stops it one move early.

The diagrams show Sente’s four ranks only. Gote’s side works the same way.

The move-40 restriction and the move-41 adjudication

Check and checkmate are not considered during placement: nothing moves, so a player under attack could simply keep placing pieces. That means a king can already be attacked once the 40 placements are done. This site handles it as follows.

Balance Shogi

Fuseki Shogi favours Sente: between AIs, Sente wins a little over 60% of games, and the stronger the engines, the wider the gap. Fixing that in the rulebook does not hold — a rule tuned at one strength is wrong at another. Balance Shogi drops the numeric compensation and lets the players themselves weigh the first move against king safety.

The mechanism is how two people share a cake: one cuts, the other picks first (the pie rule). Here, instead of cutting, one player places both kings; instead of picking a slice, the other player chooses to be Sente or Gote. The placer does not yet know which side they will play, so they have no reason to favour either one.

Procedure

Furigoma decides who places the kings. The other player chooses the side.

1. Placer
   Move 1 — the Sente king
   within Sente’s four ranks
2. Placer
   Move 2 — the Gote king
   within Gote’s four ranks
3. Chooser
   ☗ Take Sente☖ Take Gote
   Choose a side
   the position does not change
4. Sente & Gote
   Moves 3–40 — the rest
   19 each, alternately from Sente

The placement zone, the nifu-avoidance rule, the move-40 restriction and the move-41 adjudication are unchanged. What is new: the first two moves, the choice, and one more restriction, Nihikyō, described next. The kings are already on the board, so 19 pieces each remain from move 3.

Nihikyō

During placement (moves 3–40), each file of your camp may hold at most one of your rook and lances. Dropping a rook or a lance on a file that already holds your rook or a lance is illegal. Only your own pieces count; the opponent’s rook and lances do not. From move 41 the rule no longer applies.

It applies together with the move-40 restriction. If a move that would block the attack on your king is ruled out by Nihikyō, that move does not exist. If no blocking move remains, the move-41 adjudication applies as before — and Nihikyō is not lifted. Some legal placement always remains, in every position.

The rule was added on 13 September 2026. The placement AI had come to stack its rook and both lances on one file (a “triple rocket”) in most games, a shape that scored better whether or not the opponent built it too, so more training never wore it out. Its strength lies mainly in the two lances, but banning only those would just have shifted play to rook and lance, so the rook counts as well. Shapes that can be answered by preparing a defence, such as pieces facing each other, are left alone; only stacking pieces that run along the same file is ruled out.

Who places, and who is Sente

Furigoma decides who places the kings; the choice decides the sides. The placer is not necessarily Sente. The game record keeps both.

Why it balances

One pan of the scale carries the first move; the other carries the gap in king safety.

Kings of equal safety leave the first move unpaid: the chooser takes Sente and the placer is worse off. Make the Sente king too thin and the chooser takes Gote instead. The placer breaks even only when the gap in safety matches the first move exactly.

So the balance point is set by the placer’s own judgement on the day, not by the rulebook. A stronger opponent moves that point, but no rule has to be rewritten: no measurement, no numeric compensation. The road to this design is in How Balance Shogi came to be.

What the AI does

The AI on this site does not search, either when placing or when choosing. It reads a table once. The table gives Sente’s winning rate for a king pair — Sente’s king here, Gote’s king there, both sides then playing on to the end — for all 36 × 36 = 1,296 pairs.

• Placing: draw one pair at random from the 48 closest to even. Not narrower, so the AI does not open the same way every game.
• Choosing: take Sente if the pair’s value is above 50%, Gote if below.
• From move 3: the placement policy network puts down the rest. It was trained under the rules before Nihikyō and chooses among the moves that remain legal.

Those 48 pairs are valued by real games rather than by an engine score — over 600 games each. The table itself is below. Every value in it was measured under the rules before Nihikyō and has not been re-measured.

A king on the front rank (nearest the opponent) is by far the worst square, and the back-rank corners are the best. The spread between the best and worst pair is several times the first-move advantage, so the king squares alone are enough to balance it, with room to spare. How the table was built — and where it was wrong — is in the column.

The three rule sets side by side

Game record format

A game is written as USI drops separated by spaces.

P*7f means “drop a pawn on 7f”. In Balance Shogi, one extra token follows move 2: choose:sente or choose:gote. Paste a sequence under “Game record” in the menu to replay it.

SFEN during placement is a Fuseki Shogi extension with kings in hand and cannot be read by ordinary shogi software. From move 41 it is standard SFEN.

Sources

• Fuseki Shogi rules: shogitter (Japanese)
• Balance Shogi: this site’s own rule (source)