That brave guard is completely fucking insane. There's another video that shows it being used with a longsword where the player uses it to, first of all, block with a longsword, but then it's also a guard that sheaths your weapon automatically, but then apparently you can also decide while you're guarding to leave the stance by attacking instead of just by sheathing as was seen in that greatsword video.
Brave seems to solve one of the biggest problems with Adapt which is the damn roadie run making it tough to land counter attacks where you want (or at all in some cases). That alone could get me to switch from Adapt LS to Brave LS if the button combo for the guard isn't too tough to do and you can still get a quick low meter spirit gauge level up.