[Jay]

Soapy's also right; it's better to use it against someone that isn't guarding so they don't lose CC over a garbage effect.

That is not the right way to approach an underpowered skill. Most of this topic emphasizes on its damage output, when the actual effect should be compensating above that. If it's meant to spam tag a low res target, odds are they are a defense heavy, and aren't dodging a PG. And it costs 26 FP versus 10 FP.

The core of the issue seems to be the effect and little incentive to even rank it. It can function similar to Judgement Blade, so if a target is guarding, the damage is increased by Rank*10%. Guard Break does not properly penalize excessive (3M-7M) or casual (1M-2M) guarders at all. If the target was CC'd the turn before, you are slower, and the target decides to guard, you can set up something-- assuming you can hit the guarder (obviously no skills requiring CC). But that situation is too narrow for a skill that generally 'guard breaks'. Barring the unmarkable and guard break duration, even the paltry 15% damage boost, a target afflicted with 'Guard Break' should not be able to use the guard skill whatsoever. You can currently overlap the debuff the very next instance you get. If the skill is meant to synergize with other ghost skills, the unmarkable duration can also be lowered by one. Those are three ideas that pop out and would offer the skill more than enough for its purpose.