In One Piece during the Egghead arc, the scientist Vegapunk revealed that everything is going to sink into the sea. The news is pretty much shocking to everyone but Oda has hinted that the world will sink in most of the arcs it might be one of the greatest foreshadowings of the Onepiece.
Roger's Crew getting ready for the end of the world
Gol.D.Roger found One Piece and became the King of Pirates by reaching the final island of the Grand Line where they get to know about the world history of 800 years, 100 years void, and Joyboy. There are higher chances that they might know that the world is about to sink. The past members of Roger’s crew Rayleigh and Crocus seem to have learnt the truth after their journey to Laugh Tale. After the crew becomes disassembled Rayleigh learns to coat ships, and Crocus learns to make Laboon a living submarine. Both created a way to live even after the world was sunken.
Shanks creating a crew with no devil fruit users
Shanks was an apprentice to Roger’s pirate who was brought up on the ship. When Shanks meets Roger after they arrive from Laugh Tale, Shanks and Roger have a teary conversation. Even after Roger finds the place where One Piece is, Shanks refuses to go there, stating he will find One Piece on his own with his crew. Shanks might know the Truth about the world getting sunk, so he made a crew without a single Devil Fruit user to survive the fall of the world.
Mary Geoise above the Sea Level
Mary Geoise is considered a place for the gods where the Creators of the world Celestial Dragons and the highest authority of the world government, Five Elders live. Mary Geoise is located at a place far above sea level where the sea water cannot reach. The five elders were said to have been living for the past 800 years and they know the history of the world.
Oda may have hinted that the Mary Geoise was constructed to protect the Celestial Dragons if the world was absorbed by the sea. This gives us a hint that people from 800 years ago knew about the Truth and created Mary Geoise to protect their lineage.
Celestial Dragons and their masks
The Celestial Dragons are always shown to wear masks which was stated in One Piece that this is the proof to the world that they are the lieage of the Gods. The mask looks like an oxygen mask to prevent them from a situation where they lack oxygen. In One Piece it was said that the creators of the world cannot inhale the same air as the slaves inhale. The chances of them knowing about the truth of the world to be sunk might be less but what if they are taught from their birth to inherently adapt to this lifestyle so they can survive the disaster that will happen somehow in the future?
Celestial Dragons Owning Fishman Slaves
The Celestial Dragons are known to own many people from different races as slaves to prove their authority and power to other people. In One Piece it was shown that the Celestial Dragons always have a particular interest in owing a Fishman as a slave than others. This may be a hint that if the world is in a drowning situation they can use the Fishman to protect themself.
Water 7's Aqua Laguna
