Bonanza.

How it goes together

The bishops are traded first, and the silver that takes back on 8h moves up to 7g. The king walks from 5i to 6h and on to 7h. The left gold steps straight up from 6i to 6h, beside the king, and the right gold comes up to 5h next to it. The 6g pawn stays on its starting square, guarded by both golds, and the 6h gold also guards the 7g silver. Two golds in a row beside the king and the silver above him: shogi-rule.com tells beginners to remember it as an L.

Move by move

The castle needs the bishops traded, so this is a real game with both sides’ moves. White plays a Bishop Exchange Fourth File Rook and trades on 8h as soon as Black’s king steps to 6h (the first ten moves are the Leghorn Special’s), and Black’s castle moves come in the order Japanese teaching sites give them.

Seventeen moves, nine of them Black’s. After the trade the castle takes four: the silver to 7g, the king to 7h, a gold to 6h and a gold to 5h.

What it is good against

Bishop drops. With bishops in hand, a castle is judged by the squares it leaves for one to land on, and the Japanese sources agree this one leaves few. It is quick too: four moves after the trade, with the right silver and the rook still free.

Where it breaks

The bottom rank and the eighth file. Nothing stands on 8h, 7i or 6i, the square under the king is covered by the king alone, and the 8g pawn has only the king behind it. shoginoiroha names the eighth file as the usual target, and shogi-gym warns about a rook coming in along the bottom rank. Shogi Wars calls it fragile.

When to build it

After a bishop trade, by a static rook: against a ranging rook that trades bishops early, such as the Bishop Exchange Fourth File Rook (shogi-rule.com, shogi-gym), and in the Bishop Exchange itself (shogi-gym). shogi-rule.com says professionals almost never play it. Move the 5h gold up to 6g and it becomes the Half Yagura.