Strawberry.

How it goes together

The left gold goes to 7h and the right gold to 5h, each one step forward from home. The king steps diagonally from 5i to 6h, between them. The rest of the left side stays where it started: the silver on 7i, the bishop on 8h, the knight and lance in the corner. The 7h gold covers 8g, the square in front of the bishop, and both the gold and the 7i silver guard the bishop itself.

Move by move

Black only, from the start position, in the order shogi-rule.com records: open the bishop’s diagonal, then the left gold, the king and the right gold.

Four moves, and you can still build on it. shogi-rule.com names the Yagura and the Anaguma as castles it can turn into, and shogi-gym shows it growing into a Silver Crown. en.wikipedia points out that, until the bishops are traded, these are the Helmet Yagura’s squares except for the silver, which in the Helmet ends up on 7g.

What it is good against

Speed. Four moves give the king two golds, and you are free to turn the shape into something bigger later. The left gold covers 8g, so an early rook-pawn attack on the bishop’s head meets a defender.

Where it breaks

Thin cover. Only two golds stand beside the king, and the bottom rank is open: 6i is covered by the king alone, and a rook or silver dropped low is hard to meet. shogi-gym shows a silver dropped between the two golds once a dragon reaches the bottom rank, and one Japanese page warns that you cannot afford to give up your rook. The 7f pawn has no defender at all. shogi-rule.com says it does not suit a long game unless you develop it into another castle.

When to build it

Double Wing (相掛かり) and Side Pawn (横歩取り) games, for either player. ja.wikipedia names it beside the Helmet Yagura as a mainstream king-on-6h set-up in Double Wing Reclining Silver lines. Against a ranging rook it is a poor choice: shogi-gym says so, and shoginoiroha gives the reason, that a ranging rook attacks from the side, where the bottom rank is open.