Bishop Exchange Fourth File Rook.

Ranging rook, a Fourth File Rook · castles into Half Mino · 角交換四間飛車 kaku kōkan shikenbisha

The idea

The Bishop Exchange Fourth File Rook swings the rook to 6h without first closing the bishop’s diagonal. The usual Fourth File Rook closes it with a pawn on 6f, because an early bishop trade tends to let a static rook break through on its rook file. Here the trade is the plan.

You wait for White’s king to step to 4b and then take on 2b, so White has to take back with the silver, which then stands in front of its own king. Your left silver comes to 7g, where it covers 8f against White’s rook pawn in place of the bishop. The king walks to 2h behind a silver on 3h, the Half Mino.

Both sides now hold a bishop, so a loose square anywhere can take a bishop drop. With the bishops off, your bishop’s head is no longer a target, the game tends to be slow, and a static rook needs extra moves to build an Anaguma. The rook often swings again, to 8h, so the opening also plays like an Opposing Rook.

Either side can play it; the form with the king dug into an Anaguma is the Leghorn Special. Fujii Takeshi won the 2014 Masuda Kōzō Award for it.

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 7f and White’s 3d, swing the rook to 6h with the diagonal still open.
• Walk the king toward the right. When White’s king steps to 4b, take on 2b, so White has to recapture with the silver. Do not wait for the king to reach 3b, because then it could take back itself.
• Bring the left silver to 8h and then 7g, where it covers 8f.
• Finish the Half Mino: king to 2h, silver to 3h, with the gold on 4i.
• Then pick the attack from White’s setup: swing the rook to 8h and push 8f with the silver behind it (the reverse Climbing Silver), play on the seventh file, or attack from the fourth-file rook.

What to watch for

• White exchanging the rook pawn before your silver reaches 7g. Take on 2b and drop the bishop on 7g: it hits the rook on 8f and the silver on 2b at once.
• Bishop drops. Both sides hold a bishop from early on, so every gap counts: shogi-joutatsu warns that lifting the silver to 3h before the king reaches 2h leaves 2h open for a dropped bishop.
• White’s 7d pawn played in advance. It lets White meet your 8f push with a knight on 7c. The sources then move the attack to the seventh file, with the silver to 6f and the pawn to 7e.
• Swinging straight to 8h without stopping on 6h. That is the Direct Opposing Rook, a separate line, and it allows a White bishop dropped on 4e.

What it is played against

A static rook. The answers the sources name are the 7d pawn with a knight on 7c against the reverse Climbing Silver, a Reclining Silver setup with the pawn on 6d and the silver on 6c, and leaving the rook pawn short of 8e, which takes away the 8f break.

Fujii’s book has chapters on the Reclining Silver and on the held-back rook pawn. An Anaguma is possible but slow, because the silver that took back on 2b is in the way, and with bishops in hand a lopsided castle leaves squares for drops.