Brave points are generated based on damage dealt and are normally given to the attacker. Attacking with a class advantage deals more damage, but gives the defender the brave points instead. Check 
	
	You must be registered to see the links
 for more info and the class matchup chart.
Critical hits are a completely separate system based on a unit's LCK stat. Each point of LCK gives a 5% base chance to crit. Crits deal double damage, cancel/interrupt enemy skills that are charging, and ignore DEF, which is often the only reason why Siegfried can take damage at all (also why crit damage reduction items are great on her).