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.
One interesting Naruto Groudon fanfiction could be where Groudon somehow ends up in the Naruto universe. Maybe Naruto has to find a way to send it back while also dealing with the chaos it causes. For example, Groudon's presence might disrupt the natural chakra flow, and Naruto, with his determination, tries to communicate with it using his unique ability to understand others.
One common theme is power. Since Groudon is a very powerful Pokemon, in fanfiction about the female Groudon, her power is often explored, like how she uses it or struggles with it. Another theme is identity. As a female in a world where male counterparts might be more prominent, she often has to figure out her own place and identity. For example, in some stories, she has to prove herself as a strong leader despite being a female Groudon.
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.
One popular 'kyogre x groudon fanfic' is 'The Clash of Titans'. It really delves into the relationship between Kyogre and Groudon in a unique way. The story sets up an interesting scenario where they have to work together despite their natural enmity. It's full of action and also some great character development.
The Rebirth of the Primordial Sage was a doujinshi novel that told the story of the protagonist being reborn in the Primordial World and becoming a saint. The protagonist used his understanding of the situation in the Primordial World to lead the dragon race out of the predicament and become a saint. The detailed plot and full text of the novel can be downloaded for free or read online.
Well, it's the combination of two very iconic elements from the Pokémon world. Ash, the determined and often underestimated trainer, going up against the powerful and legendary Groudon. It could be interesting to see how the author portrays Ash's growth in the story. Maybe he has to overcome some personal doubts or face new challenges in order to catch Groudon. Also, the way the Pokémon world is described during the encounter, like the environment where they meet and the reactions of other Pokémon around, can add a lot of depth and interest to the fanfiction.