Tokoyonokuni

Tokoyonokuni is an ancient known in folklore as the "immortal lands". It is believed to have been the first sky island. Despite being an island, it resembles a floating castle of sorts; a black fortress that harbors entire ecosystems within its confines, along with strange glyphs that run all along the outer surfaces of the island. While its existence is known only in folk stories, a sky island located in the highest realms of the atmosphere, reaching heights deemed impossible for any known sky island, was discovered and subsequently became a secret base of operations for Fleet Admiral Kurama and his Inner Circle.

History
According to what had been deciphered from the ruins found within the island, Tokoyonokuni was the first island to arise from the ground below and soar to the skies above. It was considered to be a land blessed by the gods, and so many warrior tribes of ancient humans strove to conquer it, engaging in centuries of bloody warfare. These tribes had done such heinous things toward one another, all desperate to claim this island they believed god itself resided within, and some of the worst acts imaginable were performed toward enemy tribes; one particular action, as noted in the remaining historical records found there, was that some enemy tribes were captured, from warriors to civilians, and were forced to bury their own loved ones alive and while then digging their own graves before being mercilessly killed. Centuries of such horrible crimes caused the island itself to be drenched in the hatred, regrets, and pain of all those who suffered in trying to take Tokoyonokuni for themselves.

Overview
Kurama notes that it feels as though the island itself is alive, "seeping with overflowing Haki". He deduced, given the stories and history deciphered from the ruins, the wills of those that died and those that were buried alive had imprinted onto the island, and over the course of several centuries, those infinite life energies have continued to maintain the existence of this mysterious land. He theorized that this may be the reason why Tokoyonokuni is so far up in the atmosphere, that the wills and hatred that saturated these lands actually pushed it up higher into the skies, as if the ones who had passed away are striving to reach heaven and finally lay to rest.

Though he currently maintains the island as a base of operation for those select few in his inner circle, Kurama requested Trevisani Klaus to work on a method in weaponizing the sky island itself as a sort of moving air fortress. If possible, the Fleet Admiral believes this to be the key that will "end the war once and for all".

Behind the Scenes
In Japanese mythology, Tokoyonokuni (常世国, "Eternal Land") is a mythical country that is associated with the land of the dead. While still a plan in the works, for far future events, the author intends to have this serve as an important plot device for a future story.