Rapid attack (kyusen)

What it looks like

Kyu means urgent or quick and sen means battle. The classic case is Static Rook against Fourth-file Rook: Black builds only a Boat castle, king on 7h, which takes few moves, then raises the right silver through 4h and 4g and breaks with pawns while White's Mino may still be incomplete. Climbing Silver and the Right Fourth-file Rook are other plans with a rapid-attack spirit.

Trade-offs

Speed is the whole point: every move spent attacking is a move the opponent has not yet used for defense. The cost is that the attacker's own king is lightly protected too, so a rapid attack that fizzles often leaves the attacker worse off once the defender's pieces come into play.

The defending side usually keeps its castle simple, trades pieces when it can and looks for a counterattack on the file where the attack arrived.