Invincible.

How it goes together

The king stays on his starting square, 5i, between the two unmoved golds on 6i and 4i. The rook swings to 5h, directly above him, and the two silvers step up beside it to 6h and 4h. All nine pawns are where they started. From the front it is thick: 5g is covered by the rook and both silvers, and 5h by the king and both golds. Everything else is thin. The silvers on 6h and 4h stop the rook from moving sideways, and nothing guards the pawns on 8g and 2g or the bishop on 8h. ja.wikipedia says the origin of the name is unknown.

Move by move

Black only, from the start: one rook move and two silver moves, in the order ja.wikipedia, en.wikipedia and the Japan Shogi Association’s column give.

Three moves. Every gold and silver and the rook already stand beside the king, so the only way on is to rebuild. Both Wikipedias list the ways: as a castle, the Gold Mino, the Kimura Mino or the Right Yagura; as an opening, Crab Silvers (カニカニ銀), the Silver Horns Central Rook (ツノ銀中飛車) or the Pinwheel (風車).

What it is good against

Speed, and the front. It takes three moves, and both Wikipedias say it is solid against an attack straight down the centre. Between beginners it can win games (shogi-gym).

Where it breaks

Almost everything else. It breaks two proverbs at once, avoid the unmoved king and keep king and rook apart (both Wikipedias). The king never leaves the centre, where the fighting starts (shogi-gym). The silvers block the rook’s sideways moves, and the second- and eighth-file pawns hang. The bishop’s head is thin, and guarding it with a gold on 7h breaks the compact shape; a silver that goes forward to attack leaves the castle, so it is hard to build any attack at all (the JSA column). ja.wikipedia calls it very weak from the side.

When to build it

Never on purpose. It is a beginner’s shape and a joke among stronger players: ja.wikipedia files it with the joke openings and castles (冗談の戦法・囲い). Imaizumi Kenji wrote that he played it as a child, and the women’s professional Satomi Kana once built it in an official game and went on into a Duck (ja.wikipedia).