Location
Just after the first boss, Rogue, keep running right a few rooms.
Properties
Holding the attack button will make Shin focus, causing a cone to appear in front of him going the direction the player presses on the dpad. Positioning an enemy or a target in the cone and releasing the attack button will cause Shin to teleport-dash to the other side of the enemy/object while slashing it, anime-style. Shin appears at a position relative to the target depending on what direction you are holding, not necessarily the direction of the target from Shin himself. So as an example, if the player is holding right and hits a target above them, they will appear to the right of the target.
Homing dash can be instantly charged by rolling and pressing/holding the attack button during the roll.
Trivia
Shin can jump while charging a homing dash