United Lands of the Poseidon Ocean
The United Lands of the Poseidon Ocean (ポセイドン海の連合国 Poseidon-kai no Rengōkoku) was a kingdom in the Yu-Gi-Oh! ZEXAL anime consisting of several islands connected via bridges. It was united by Nash, who became the monarch of the land and was well-loved by his people.
The kingdom was eventually attacked by Vector, who led a large fleet of ships in an effort to destroy and loot the land, aided by a group of "Gorgonic Guardians". They were initially outmatched, but eventually Nash ordered the land's soldiers into battle equipped with mirror shields, which were able to defeat the gorgons by reflecting their own weapons back at them. In response, Vector performed a blood sacrifice to call forth the ocean god, Abyss, which turned the tide of the battle to his favor. Nash's sister Marin rode up to where the ocean god stood and was grabbed by its gargantuan hand. Despite the intervention of Nash's friend, a knight named Dumon, Marin did not want to be saved and instead pitched herself into the depths to call forth a goddess in order to purify Abyss.
Vector's army fled after the god was turned to Nash's side. As they fled, they destroyed several villages. Nash and Dumon ordered their army to give chase. At one of the villages, they found a survivor in a girl who resembled Marin named Iris. She accompanied them and became fast friends with Nash. Nash led his army against Vector's using Abyss. Eventually, Vector retreated into a temple. Nash gave chase and Vector challenged him to a Shadow Duel to settle things. Nash agreed, but the terms of the Duel dictated that the more monsters that are sent to the Graveyard, the more of the Duelist's army will die. Though Nash defeated Vector's "Gorgonic Guardians" using "Number 73: Abyss Splash", his entire army was decimated due to Vector's mill strategy. Dumon survived, but Iris did not. The army was absorbed into Barian World due to the chaos.