Yagura Anaguma.

How it goes together

The golds and the silver stand as in a Gold Yagura: golds on 7h and 6g, silver on 7g, pawns on 7f and 6f. The lance has stepped up to 9h and the king has dropped into the corner square it left, 9i, so the Gold Yagura’s king square, 8h, is empty. The 7h gold guards the 6g gold and the 7g silver, but nothing guards the 7h gold itself: in a Gold Yagura the king did.

A Yagura Anaguma is a Yagura with two more moves: the first twelve below are that castle.

Move by move

Black only, from the start position: our Gold Yagura’s twelve moves, then the lance up one square and the king into the corner.

Fourteen moves. Japanese sources show it going further, with a gold to 8h, or the silver to 8h and a gold to 7g; ja.wikipedia says players call that last form the complete Anaguma (完全穴熊).

What it is good against

Distance. With the king on 9i the opponent needs many moves before a check, so you can keep attacking while they break in (shougi.jp, shogi-gym). Shogi Wars says the Anaguma’s great strength, being far from the battle, still holds. It costs only two moves from a Gold Yagura.

Where it breaks

Loose pieces and the edge. Shogi Wars says the pieces are poorly connected and the shape unbalanced. The 7h gold has no defender, and the edge file is now the king’s: lances, knights and a rook gathered on the ninth file go straight at it (shougi.jp, shogi-gym, shogijugem). shogi-gym adds that it is not as hard as an Anaguma built against a ranging rook and can collapse to a direct attack from above.

When to build it

Double Yagura games (相矢倉) that turn slow, when the opponent has no quick attack and Black has time to spare (shougi.jp, shogi-gym). ja.wikipedia says Black often went into it from the Yagura attack with the silver on 4f and the knight on 3g before starting the fight. Four of the five sources that list it file it with the Yagura castles; shogi-gym files it with the Anaguma.