[Kameron8]

Buster Cannon, when at rank 5 because of a White Spirit, does not gain any additional defense removal. Following the scaling of 10%,30%,60%,100%, rank 5 of the skill should remove 150% of the target's defense. This sounds absolutely ridiculous to report at a glance, but it does impact how bosses should be effected by the skill. Someone investing into the spirit should realistically be seeing 75% defense reduction versus boss creatures, as well as removing any lingering defense on players with buffs/passives that apply after the debuff by placing them into the negatives.

(Negative defense is treated as 0, if memory serves.)

[Neus]

Percentage modifiers from status effects like this apply when status effect modifiers do, which is after item effects, quest stamps, and class bonuses, but before everything else. It also applies to the base stat, not the modified stat, due to a change made a long while ago. Any oddities you're seeing is likely due to that.

[Kameron8]

That's about what I figured as far as functionality goes, however, I'm unsure if you're going to tweak the white spirit to function with Buster Cannon.

[Neus]

The scaling is set by the rank of the skill.

I guess I can't think of a good reason to say no to the spirit scaling, even if I don't necessarily think it should work that way, so we'll give it a try.