Oceanus, Realm of the Sea, is a vast expanse of water, dotted by islands, filled to the brim with all kinds of life, great raft-cities, and giant ships. Oceanus is not a place of darkness and death, but a place of life and diversity.
Oceanus is a crossroads of Titanrealms, due to its Avatars being - relatively - less violent and more fluid than in other Realms. It is linked to Patala, accessed through delving in the depths of Oceanus, if one manages to get past the giant sea creatures which make up most of Oceanus' wildlife, the fields of deadly jellyfish the size of small countries, and the tolls set up by the more organized Titanspawn.
Oceanus can also be accessed through Terra, though the way is guarded by creatures of Gaia residing in the Swamp Kingdom of Sli'eth, ruled by the former Goddess Heqet, now minor Avatar of Fertility vassal to Gaia. Heqet herself is relatively friendly to the Gods - especially her former brethren among the Neter. But her alliance with Gaia means that any Gods entering Heqet's realm needs lavish gifts of tribute if they want to appease her. Nevertheless, this has led to Sli'eth seeing a large concentration of God-aligned beings.
Amaunet also knows entrances into Oceanus, though these entrances lead directly from the Tempest Layer of Amaunet to Yam's dangerous realm of the Raging Sea - anyone attempting to ride the storm better do so with the assent of the Titans, or risk being shred to pieces before feeding the hungry creatures of Oceanus.
Internal Politics and Culture
Oceanus is relatively peaceful and thriving thanks to Sedna's influence and political alliances. Though Yam is the most powerful Avatar, the staunch support of the Gods towards Sedna, the ever-present menace from the depths of Patala, and the newly-ascended Titan Tlaloc acting as a peaceful buffer between Yam's primary ally, Huracán, all work towards Oceanus being a relatively stable realm.
Yam's Titanspawn are highly organized, and militarily-minded, with legions of water-chariots pulled by seahorses and mermen infantry forming the bulk of his forces, reinforced by sea monsters of all kinds. Various kingdoms are rival between each other for Yam's favor, and part of obtaining that favor is to bring trophies at the Avatar's feet. Those trophies are collected from expeditions into Patala or Terra, attacks on other Avatars of Oceanus, or war against the Gods themselves, which leads his forces to be spread throughout all parts of the Overworld.
Meanwhile, Sedna's people live in gigantic Barge-Kingdoms, flotillas of ships shared by tribes, living, growing, travelling together and living off the sea. Trade with creatures closer to Terra - and the Gods - allows them to have all they need, and the matriarchal tribes are relatively united, especially knowing they are the bastion of peace in an ocean of turmoil.
Most of the Gods' outposts are based in Sedna's Barge-Kingdoms, with most Pantheons having an ambassador at her Court to ensure her good graces. However, some Gods have grown closer to Yam. In particular, Poseidon and Ryujin have proven themselves to wield and respect the destructive power of the Sea against those who do not share that respect, and have the closest thing Yam holds to friendship. Though no official alliance exists, it is not unheard of to have groups of Godborn find themselves on opposite sides of a battle between Yam and Sedna.