Many weapons have some sort of counter-attack, usually in the form of a ‘ddd’ technique (eg ‘rd’, ‘rd’, ‘rd’ to perform right handed). These counter-attacks operate exactly like defensive techniques, except that when you successfully defend they follow up with an attack.
This follow-up attack is usually automatic, except for swordbreakers and tiger claws, which give you 5 seconds to choose a response - allowing you to disarm your opponent, break their weapon, or perform an attack. A main gauche also has the ability to lock the weapons it parries, which freezes the main gauche and the attacking weapon for 5 seconds (very useful vs two-handed weapons).
A counter-attack can only be dodged, or blocked by shields. After execution it will need to be reset, although it still provides a regular defence.
It’s important to remember that the counter-attack waits until triggered by a successful block or parry, so after setting it up you shouldn’t perform any other commands with that location or you’ll lose the counter-attack.
See also: combo interleaving techniques tutorial