[Comartemis]

Ah... not quite. Better spell resistance applies against spells cast by mages stronger than her. They'll still penetrate her shielding, but they'll have a harder time of it and not as much energy will get through to her. Spells cast by mages below her rank will have their effects significantly decreased or even canceled altogether if they meet one of her shields, and offensively-used void magic can be used to break shields, like I mentioned, though the strength of the shield still factors in significantly; this isn't an Instant Shield Killer like what SLB+ has, or Arf's Barrier Break spell, just an enhancement to offensive power when applied against magical defenses.

Keep in mind, everyone of a mage rank lower than Asuna is probably going to be a mook or otherwise cannon fodder--at least at first, with her starting out around B-rank with the Forwards--who wouldn't have much chance against "hero units" anyways. And obviously Void magic has no effect against non-magical attacks like what Jail's toys are working with.

Basically this grants Asuna enhanced offensive melee and defensive power when matched against energy-type spells. Physical spells are less affected by this ability. So the net effect is to make Asuna noticeably stronger than the average mage of a similar rank in certain situations. This is hardly a catch-all defensive ability like the Saint's Armor; it has plenty of weaknesses waiting to be exposed.