Yonenaga Rapid Attack Yagura.

Static rook, played by White · castles into Crab, on White’s side · 米長流急戦矢倉 Yonenaga-ryū kyūsen yagura

The idea

This line is White’s. The Yonenaga Rapid Attack Yagura is a way for White to take the lead in the Yagura instead of waiting. ja.wikipedia says professionals played it a great deal in the mid-1980s, after Yonenaga Kunio made it his own and won the Jūdan title from Nakahara Makoto with it.

You castle in a Crab, king on 4a, golds on 3b and 5b, silvers on 4b and 6b; you leave the bishop on 2b looking down the long diagonal, push the pawn to 6d and jump the knight to 7c. The attack comes on the 6th file, with the 8th-file pawn and the knight joining in, and the aim is to break through and make a horse.

Black’s answers were worked out over time: ja.wikipedia says an early bishop retreat to 7i proved effective, and professionals then dropped the opening. This line shows that defence.

You attack in full, and Black holds with a pawn dropped on 6f, a good move, says the line’s one source, which adds that the same position arose in the first game of the 2004 Ryūō title match, which Black won.

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

• Castle in a Crab: king 4a, golds 3b and 5b, silvers 4b and 6b. Push the 7th-file pawn and the rook pawn to 8e.
• Push the pawn to 6d and jump the knight to 7c, keeping the bishop on 2b.
• Bring the left silver to 5c, then break with the pawn to 6e.
• After Black takes, add the pawn to 8f and the knight to 6e, and take on 8f with the rook.
• Answer Black’s 2nd-file trade with a pawn dropped on 2f, then take the silver on 6f with the bishop and drop a silver on 5g.

What to watch for

• Black’s bishop on 7i. It trades the 2nd-file pawn and comes out to 4f, where it watches your attack.
• Attacking at once. The source’s other line pushes the pawn to 6e on move 26; you win there only because Black later takes a pawn on 7e, and the source gives the pawn to 3f as Black’s correct reply.
• Your own king. A Rapid Attack Yagura leaves your king thin; once Black survives the attack, the counterattack is fast.
• The other form. ja.wikipedia’s Yagura article shows a Yonenaga line from 1986 in which the silver comes out to 4d and you attack with the pawns to 5e and 6e; Fujimori Tetsuya’s later version puts the rook on 8c.

What it is played against

Black, building a Yagura, keeps the king on 6i rather than walking it into the castle, pulls the bishop back to 7i early, trades the 2nd-file pawn with it, and meets the 6th-file break by taking.

Against the full attack in this line Black gives back material and finds the pawn dropped on 6f. In the late 2010s Black also used this attack against White’s Static Bishop Left Mino Rapid Attack.