Luster class, in-game class skill description.
The English skill description of Sub-Luster Gunblade Boost skill is somewhat misleading. The in-game text says,
"Boosts the potency of your Main Class when a Gunblade is equipped. This skill can only be used when a Sub-Class is set."
But this should be something like,
"When a Gunblade is equipped, boosts the potency depending on your Main Class. Usable only by a Sub Class."
There are two problematic points. The first is that the potency boost multiplier given by this class skill varies with what the main class is. This is not shown in the current English text, I think. The second point is in the second sentence (This skill can only be used when a Sub-Class is set.). If we carefully read it, we can see that its not talking about a case of Luster main as Luster can't have sub classes. But why the current English text says that in such an indirect way? Can't it just say as the same way as other numerous "main class only" skills? ("This skill can only be used by a Main Class.")
The original Japanese text just say these "main class only" and "sub class only" in the same way ("このスキルはメインクラスのみ適用される。" and "このスキルはサブクラスのみ適用される。").