[Autumn]

What I'm looking for here is mostly an excuse to roleplay transformations that isn't just only an aesthetic feature, some sort of skill that would give you a buff that explains going beyond normal means, like I mentioned in the OP, I do not expect a global transformation-type ability to be overtly powerful, and would rather it be a special ability that would simply give me an excuse to roleplay the way I'd prefer to.

For example this could be a 10 star item effect of like a ring or helmet, this would probably fit in most people's builds regardless of their class and weapon setup, and also have a cost of 1 of your 10 star item slots.