For Kyogre, it could be characterized as a powerful but somewhat solitary being. It's protective of the oceans and views any threat to the seas as a direct attack. It's majestic and its movements are fluid like the waves. Groudon, on the other hand, is a force of the land. It's stubborn and proud, believing that the land is the most important part of the world. It's slow to trust but once it does, it's a loyal ally.
In a fanfic, Groudon can be seen as a proud and territorial being. Since it represents the land, it guards its territory fiercely. It has a sense of honor and dignity associated with its role as the keeper of the earth. Kyogre can be characterized as a wise and ancient entity. It has seen the ebb and flow of countless years beneath the ocean waves. It is patient but when provoked, it can call upon the power of the entire ocean to defend itself. They both can be shown as having a mutual respect for each other's power deep down, even though their natures often put them at odds.
Typically, in fanfiction, Kyogre is often depicted as a powerful and majestic being. It may be shown with its control over water being even more extreme, like creating massive tidal waves or controlling the very essence of the ocean's currents.
I would recommend 'The Legendary Bond: Ash and Kyogre'. In this fanfiction, the author does a great job of showing the connection between Ash and Kyogre. It starts with Ash having a strange encounter with Kyogre and then evolves into a full - fledged adventure. There's also 'Ash's Encounter with the Mighty Kyogre' which is more action - packed and shows Ash in some intense battles while trying to protect Kyogre.
Well, for Toxapex in the story, I'd say a great moveset is Venoshock, in addition to Recover, Toxic Spikes, and Haze. Venoshock deals more damage when the target is poisoned, which pairs well with Toxic Spikes. Recover, of course, is there to keep Toxapex alive. Haze can be used to clear out any stat changes on the field, which can be really handy in certain story battles.
One effective moveset for Cofagrigus could be Shadow Ball, Will-O-Wisp, Protect, and Toxic. These moves give it a mix of offensive and defensive capabilities.
Well, there are a lot of great things about Pokemon Ash and Kyogre fanfictions. One aspect is how they expand the Pokemon world. They can create new adventures for Ash in the context of Kyogre. Maybe Ash has to figure out how to communicate with Kyogre on a deeper level. Also, the fanfictions might introduce new characters who are also interested in Kyogre. It's all about creativity and taking the existing Pokemon lore and adding new twists to it.
In fanfic, female Kyogre is often depicted as more nurturing. For example, she might be shown taking care of baby Pokémon in the ocean. She can also be more empathetic towards other sea - dwelling creatures.
The fanfiction where Kyogre saves Ash could also have a deeper meaning. It might symbolize the power of nature (represented by Kyogre) coming to the aid of a determined trainer (Ash). In the Pokemon world, trainers and Pokemon often have a bond that goes beyond the physical. So when Kyogre saves Ash, it could be seen as a manifestation of that bond on a grander scale. Also, the story might show how Ash's kindness and respect for Pokemon throughout his journey have earned him the help of such a powerful being like Kyogre.
A great fanfiction idea could be a time - travel story involving Groudon and Kyogre. A trainer travels back in time to the era when Groudon and Kyogre first started their feud. The trainer tries to prevent the feud from ever starting, but in doing so, he accidentally disrupts the balance of nature in that time period, leading to new and unexpected challenges.