Fourth-to-Third File Rook.

Ranging rook, played by White · castles into Mino, on White’s side · ４→３戦法 yon-san senpō

The idea

This line is White’s. You would like the open-diagonal Ishida that Black plays in Masuda’s Ishida, but going straight there a move behind is risky: if your rook goes at once to 3b, Black can trade bishops and drop one on 6e, which attacks 4c and 8c together. Tobe Makoto’s answer, worked out from Shima Akira’s 3-4-3, is to stop on the fourth file first.

With the rook on 4b, 4c is guarded. The king then walks to 7b, where it guards 8c, and only then does the rook swing on to 3b, with the pawn to 3e and the rook up to 3d to follow. ja.wikipedia says White has lost a move but reaches a Masuda’s Ishida game.

Because the pawn push waits until after the swing, you can still choose an ordinary Third File Rook if Black closes the diagonal. The line is shogi-joutatsu’s, after Tobe’s 2013 book; moves 11 to 14 have that one source in this order. The Mino is the castle it heads for, but the line stops with the king on 7b.

How it goes together

Both sides’ moves are shown, because this opening is an agreement rather than a system: one player cannot reach it alone, so a one-sided list of moves would be a fiction.

The plan once you are set up

• After Black’s 7f and 2f, swing the rook to 4b with the diagonal open.
• Walk the king to 6b and 7b.
• Swing the rook on to 3b.
• Push the pawn to 3e and float the rook to 3d. Close the diagonal with the pawn to 4d when you want a calm game.

What to watch for

• Black’s pawn to 2d before Black’s king has moved. Take with the pawn, and when the rook comes to 2d, trade bishops and drop one on 3c: it attacks the rook on 2d and the silver on 8h.
• The same pawn push after Black’s king has reached 7h. Now the king guards the silver, so the bishop drop is no fork. Offer the rook trade with the rook to 2b instead, and after Black drops a pawn on 2c, keep the lance guarded with the rook on 1b.
• The lost move. If Black uses it to castle well, there is no hurry; the sources accept a slower game.

What it is played against

A static rook that has pushed the rook pawn and keeps its own bishop’s diagonal open. shogi-joutatsu and thirdfilerook.jp both name the pawn push to 2d, at one moment or another, as the attack to be ready for.

If Black closes the diagonal instead, the swing to the third file becomes an ordinary Third File Rook.

Where it came from

3-4-3 (３・４・３戦法)

Shima Akira’s plan from his 2002 book on the ranging rook, the one Tobe’s opening grew out of.

The name follows the files: the pawn goes to 3e first, on move four, then the rook stops on 4b, and once the king is on 7b the rook swings to 3b. thirdfilerook.jp gives the reason for the stop: after the pawn to 3e, if Black answers with the silver to 4h you can swing to 3b at once, but against the king to 6h the direct swing loses to the bishop trade and a bishop dropped on 6e. ja.wikipedia adds that the stop on the fourth file also helps against the Climbing Gold, the Ishida’s old enemy.

The difference from Tobe’s order is the pawn: pushing it early commits you to the Ishida, while the Fourth-to-Third File Rook keeps the choice open until the rook has swung. Both boards are ja.wikipedia’s diagrams.