It's not that detailed but here is a clunky rough draft of a mini-story:
Hai-Zo (Tai-Yu) was a man born in the land of Qin. Much like Wano, Qin was an ancient country with centuries of culture and tradition, but it was unaffiliated with the WG; it wasn't an ally. The reason being was not only the strength of it's people but also what guarded it. An ancient sea beast that lived near it's shores for centuries, named Yushe (Jade Serpent), guarding the land and it's people for one reason, the emerald pearl. It was a gigantic pearl, nestled deep within the land, radiating an enchanting energy which drew the beast to it, like crows to a pearl. The Qin folk had worshiped the Emerald since time immemorial, believing that it was the source of their health, strength, longevity and fertile land. Not only was the Yushe instinctually tied to the pearl but so were the people of Qin; born with a distinct scent granted to them by the pearl, they were exempt from the wrath of the beast; rather, they were protected by it as it saw them as offspring of the jewel it lived to guard. Hai-zo was a marine, with the discipline and strength of a Qin in his blood, alongside a powerful rock logia devil fruit, he rose up the ranks making his way to Fleet Admiral. The newly appointed FA was loved and respected by the people. He believed in "immutable justice" solid and unchanging, he didn't discriminate, if there was someone who needed saving, he would save them, such a day would soon come.
On the front lines of the new generation there was a rising star, fool-hardy and hot headed, the 29 year old Drummond D. Baron was ravaging through the new world. Not only was he a member of the infamous D clan but he also possessed a powerful awakened devil fruit, the Sabi-Sabi (rust fruit). This young pirate had amassed a fleet of 8 thousand strong and a bounty of 2.1 billion. But his newest exploit would put an end to his terror, as he set his eyes on the Emerald pearl. With his fleet he sailed to Qin, but the pirates would never step foot on it's soil, for the Yushe ravaged them and swallowed them whole. It seemed like the threat was eliminated, but the curse of the D's reaches beyond the grave. Among the devoured cargo on Baron's ship there was a Devil fruit, it held the power of the mythical Taotie. The Yushe had been cursed by the sea, for now it had turned into a raging, gluttonous beast. No longer is it a guardian, but a calamity upon the land and it's people. It pounced, bit, mauled, ripped, shredded and devoured; the men, women and children of Qin, each of them a warrior in their own right, were incapable of drawing a drop of blood from the monster. The once harmonious land had turned into a symphony from hell, with no savior.
Back at the Navy HQ, the newly appointed Fleet Admiral is seated at his desk hidden behind piles of paperwork. As if a sign from the divine, a chill ran down his spine, the same feeling a distant mother has when her child is in danger. Acting upon this instinct he opens his desk drawer to see two burning vivre cards, his mothers and younger brothers. He rushes to the communication center, but a young marine stops him mid-way, he informs Hai-zo that they intercepted reports from pirates who fled Qin's shores about what transpired. Hai-Zo frantically calls the Commander-in-chief, Daiken, requesting permission to intervene, but he reminds Hai that Qin is not an affiliate of the WG and that they are under no obligation to protect it, the losses would also be too great. But this doesn't deter him, his sense of justice wouldn't allow him to abandon anyone, let alone his own people. Hai-zo takes a ship and heads to Qin, the journey would take him a full day of continuous sailing on the fastest of vessels. As Hai-zo draws closer to Qin he already sees a preview of it's state, the proud mountains that once stood as pillars have been flattened, smoke blackened the sky above and haunting screams could be heard from afar. Once he reaches Qin he dashes with lightning speed easily covering the distance between himself and the beast. He strikes it with a earth shaking attack before it could bite through another town. What followed was a battle of epic magnitude, but Hai-zo was fighting alone and this threat was too much for him to deal with while innocents were present. Using a great deal of his remaining power he creates a massive Ark for the surviving Qinfolk to board and escape.
Now only he and the beast remain, with no hope for reinforcements he continues to fight with all the strength he has left. Days upon days he battles, but the beasts fury never waned. Hai-zo's body was beaten and broken, kept alive by his sense of duty, he knew there was only one way to victory. Using his awakened logia powers he starts to reshape the entire country; mountains, rivers and valleys all bending to his will, molding it into a prison for the beast. To stop it from eating it's way out, he takes the sacred Emerald and forces it into the beasts maw; silencing it's bite forever he can now trap it in the Qin prison. Hai-zo begins to mold the country around the Yushe, trapping it and himself. Qin groaned in protest, cracks split the land and gave way, weakening it until it sank slowly into the sea.
When news reached the WG, they wasted no time to cover it up, re-writing history to tarnish the name of Hai-zo. They started spreading lies about how he attempted to use his position of power to take the Emerald for himself, conqueror Qin by force and ultimately met his demise against the Yushe. The world moved on but the truth remained in the hearts of the Qinfolk. Adrift and grieving, they eventually landed on foreign shores. But they were a persevering people, from the stones of the Ark they rebuilt their civilization, a place born from the soul of its savior. They called it Bei Sheng, the land of sorrowful rebirth.
