I'm happy the appeal finally clicked with Kou-chan! I guess it was a case of "the loli doth protest too much methinks". I mean if Kou really hated all the dress up times we would've seen brooding, despair and genuine anger/resentment. Not pouting, whining and flimsy protests. Experiencing it on her own terms instead of Natsuki breathing down her neck was all that was needed.
Now I'm wondering if on some deep unconscious level Kou was jealous of all his friends this whole series and just never admitted it to himself.