>Pufferfish (known as fugu) was banned in Japan throughout the Meiji period due to it's dangerousness
>Was historically used as a poison
>The Emperor is forbidden from consuming or even touching fugu
Couldn't really find anything specific, but all of this could explain H-Qwilfish's Dark Typing. It lost it's Water Type because it's no longer in the sea, but on a plate, and it's a forbidden dish.