With the confirmation that the Holy Knights have Deep Sea contracts, it’s more or less confirmed that the Gorosei have Abyssal Sea contracts.
The Gorosei’s Yokai forms seem to be derived from their contract and are not presented as devil fruit abilities when introduced. So it stands to reason that we haven’t actually seen a devil fruit user with the deepest level of contract.
Naturally a question arises: what happens when a devil fruit user makes an Abyssal Sea contract? Does the demon form override their fruit ability? Do they stack?
I’m actually going to go out on a limb here and say that it’s not possible for a devil fruit user to also get an Abyssal Sea contract.
The Gorosei’s Yokai forms seem to be derived from their contract and are not presented as devil fruit abilities when introduced. So it stands to reason that we haven’t actually seen a devil fruit user with the deepest level of contract.
Naturally a question arises: what happens when a devil fruit user makes an Abyssal Sea contract? Does the demon form override their fruit ability? Do they stack?
I’m actually going to go out on a limb here and say that it’s not possible for a devil fruit user to also get an Abyssal Sea contract.
DFs invalidate the highest level of demonic enslavement.

