The Islands World (translation meaning for "Seken no Shima") is a world of marines, sailors, and islanders as its fill with few known subcontients and many archipelagos as the oceans and seas are the bodymass around it.
They specialize in kenjutsu, chakra kyuninjutsu, sokujutsu, and possesses a great affinity for Water Style.
Most of this world's beginnings is that this world was once called the Grassland World, and early histories are that in this world, it once had a supercontinent that was with one ocean, but to the influence of humanity's greed, drug addictions, and etc. In the times as the sub continents and small islands, this world uses shipcraft and medium advanced of technology to travel through the seas and navigations and its said to have some lost treasures to distant lands and lost civilizations yet to be found or rediscovered.
Eighteen hundred and eighty years ago prior to Kaipuden, their craze obessions cause forth many evil spirits to pillage their lands as it was close to being conquered by an Adjuchas-class Menos as he requries humans to dine on their souls for power as a punishment for their sins. Then one day, a beautiful maiden with pure intent to spare the survivors of his world conquest by offering himself to be eaten (but didn't know that that Adjuchas was lying and had no intention to keep that promise). However, a man with the "samsara eyes of the heavens" came to this world and saves the beautiful maiden, and as he faces the Adjuchas in combat, he was victorious in battle as the evil spirit saw their fallen leader's spiritual pressure gone, they left the world of the living. This man was in actuality the Sage of the Six Paths, who shows the people of this world that money, status, and possessions aren't the keys to true happiness and shows them that love and understanding was the true key to true happiness as they needed others to alongside to achieve such accomplishments.
As he saved the maiden (and somehow acquired her affection to him), she ask a request to go back to his world with him as a debt for saving her, thus leaving her old homeworld.
Fifteen hundred years, as the surviving Hollows decided to seek vegeance for the master that the Sage of the Six Paths killed, by killing every human and their lands in blazing destruuctions across the supercontinent and as the people were waiting for the Sage of the Six Paths' return again, however it was too late as he already died of natural causes and with the final moments for their end to come, suddenly ten-tailed beasts came and severed the entire supercontinent, thus creating several subcontinents and many small islands as they were a part of the Sage of the Six Paths, the people decided to stop relying on the Six Paths and want to become spiritual to be a bit closer to him, but this is didn't this world from declaring war against one another as the number of conflicts are unknown.
A century ago before the start of the current story, the Hollow Axis began their long invasions in the Islands World, speading their destruction across the world as they began their long battle against the humans. As the menos-class Hollows advanced to the hemisphere, they slain the warlords of five nations as they claim victory over the humans. Somehow, the Islands World was visited by other humans from different worlds (due to they were also in combat against the Hollow Axis) combine their technology together and united their worlds' forces to become the Human Allies.