The Big Three Shogi Castles
Shogi castling involves forming a stronghold to protect the king. Most shogi pieces don’t move very fast, but as soon as a pieces start getting captured, lightning fast plays involving drops change the pace of the game. Placing your king in a castle allows you to focus on attack.
The most deadly location for a king in shogi is the square it starts on. Dead center means a dead king! Get the king off to a corner and protected, quickly.
Shogi castles keep the rook and king apart. A common tactic of advanced shogi players is setting up a split with the king and rook so that a knight or other piece attacks both the rook and king. Of course, losing the rook in such a split makes winning more of a challenge.