Crab.

How it goes together

The left gold steps up to 7h and the right gold to 5h. The left silver comes up from 7i to 6h, between them, and the king steps sideways from 5i to 6i, under the silver. The king guards all three generals, and both golds guard the silver. The bishop stays on 8h. In this order the right silver has gone to 4h, where it is free to attack; it is not part of the castle. Japanese sources say the name comes from the shape, which looks like a crab.

Move by move

Black only, from the start position. Two pawns and the right silver come first, then the left gold, the left silver, the king and the right gold.

Seven moves. The king can now step only sideways, to 7i or 5i, and the silver on 6h can still go either way: up to 7g toward a Yagura, or to 5g for an attack.

What it is good against

Attacks from above. Three generals stand in a row over the king, so a piece that lands in front of the castle on 7g, 6g or 5g meets at least three defenders. It is also quick: you can attack from it at once, or keep building and turn it into a Yagura.

Where it breaks

The side. Each gold is guarded by the king alone, so a rook that reaches the back rank, or one dropped in from the side, finds the castle open. Moving the king on to 7i helps against a rook drop, and growing the castle into a Yagura helps more.

When to build it

Against another static rook. A Yagura player passes through it, and White in a Yagura game builds it first as standard. Players also stop here to attack early: a Climbing Silver that keeps the bishops on, Yonenaga’s rapid-attack Yagura (米長流急戦矢倉), or the Eishun-style Right Fourth File Rook (英春流右四間飛車). In two-piece handicap games it is the castle of the player receiving the handicap.