[GoseiWonder]

What if wearing a Sengoku Driver not only let's you use Helheim's fruits for nourishment and power without mutating, but it also builds an immunity toward mutation?

Why did Hase struggle to remain human while Yuya just shifted? I think it's that Hase used his driver enough times that he developed a resistance to the mutagens, but not enough to save him due to his small number of henshins.

So I theorize that someone will eat Helheim's fruit to get all the power of it witout Sengoku Driver dilution and because they've used their Driver frequently enoug, they'll manage to control the mutation to their liking, making them a human/Invess Creature that can harness Overlord levels of power wile keeping their mind intact.