Ah, combat mechanics stuff is where i come in.
You probably never played with the 2handers, or at least in an overly defensive ways. Parrying an attack - as opposed to blocking or evading - drains your weapon grip. As such losing grip, and subsequently getting disarmed, happens when you defend with only your weapon.
But even that doesnt drain enough grip to drop it.
What does are the moves parry->riposte/disarm - which drain between 6-21 grip - depending on the intensity of the opposing attack - deflect attacks that are
susceptible to parry and drain their own grip.
The goal is to end with a disarm, which must be timed to coincide with an enemy attack. Doing so will fully negate the damage, puts Hiro at "advantage" status, sends their weapon flying and does ~16dmg with the counter. A disarmed enemy spends several turns attacking you unarmed, which do mostly nothing and after that will spend 2 turns going "use item->[name of weapon dropped]".
Note that even successfully disarming an opponent will drain 12-19 grip every time and I've often gotten myself disarmed when getting carried away with the preceding parry/riposte dance. Disarming also heavily relies on you being faster than the opponent so anything with poor agility should not bother (thief supremacy)
Like with real fencing, the trick here is to know the pattern of an enemy attack. If you spend too much time whiffing parries/riposte when enemy isnt attacking, or attempt them
(or the disarming) during attack that cant be parried (most notably Grand Slash, overrun and assault), you will lose your stability/grip for nothing and get hit anyway.
Also: while parry - used to enter the stance - recovers stability and disarm ends it, riposte will let you remain in parry stance, until you find an opening to use disarm, but will drain more stability with each use.
