Sorry, I couldn’t find a clear answer in the costume thread.
In the description, it reads “Costume bonus can be increased by ascending and fully leveling the costume.”
I have Rigard at 4.1, I intend to use him in his costumed form, at least for now. I do not intend to emblem him just yet. I figured I’ll work on leveling his costume because it’s faster. Since it says “…by ascending and fully leveling the costume” (not the hero), does that mean that when I max the costume, I will have the full costume bonus? I suppose I’ll get my answer when I’m done leveling his costume, but figured maybe someone has the maxed costume on non-maxed hero.