- Hundreds of years ago, the Mink tribe and the Kozuki family made an appointment. If one of them experiences hardship, they must help each other.
Whoa, I almost overlooked this interesting little tidbit. There's still a subplot left hanging from Zou over who Zunisha is, why the Minks live there, why Momonosuke is able to command it.
What if hundreds of years ago is actually a thousand+ years ago relating to the crime Zunisha was sentenced to roam the sea endlessly for? The ancient Kozuki family could posses absolute domination over Zunisha and created a home for their Mink friends as retribution. Could be the Minks just climbed on to make sure the sentence was carried out. Either way, I think the details of that involve the overall world of One Piece and the Oden flashback is still to early to answer it.
Though I wonder who could answer the question. Momo can't even read Poneglyphs, Toki probably did die in the past, so Hiyori must posses ancient Kozuki clan knowledge or whoever inherited the Time-Time fruit.