One idea could be to write a story from the perspective of a civilian caught in the middle of the Kaiju battles. Show their fear, their attempts to survive, and how they interact with the military trying to stop the Kaiju. Another could be a story about a Kaiju that has unique abilities not seen in the original lore, and how it changes the dynamic of the wars. Maybe it could be a Kaiju that can communicate with humans and tries to form an alliance against the more destructive Kaiju.
Some of the lesser - known Kaiju can also be interesting to include in fanfiction. For example, Rodan. He has his own unique abilities and personality. A fanfiction could explore his backstory more deeply, or create a new relationship between him and the other more well - known Kaiju. Anguirus is another one. He could be portrayed as a loyal ally to Godzilla, or have his own motives for being involved in the Kaiju Wars.
One popular character might be a kaiju girl with the ability to fly. Her aerial battles against other kaiju or threats are often a highlight in many fanfics. She is usually depicted as strong and independent.
A kaiju girls fanfic could also explore their origin stories. Maybe they were created by some scientific experiment gone wrong. The fanfic could delve into how they feel about their existence, whether they resent being different or embrace their kaiju side, and how they interact with the scientists who were involved in their creation.
One possibility is that the heroes would initially be in awe of Godzilla's sheer size and power. They might try to communicate with it using their unique powers related to the Greek gods. For example, if there's a hero with the power of telepathy, they could attempt to reach Godzilla's mind. However, Godzilla's primal nature might make it difficult to establish a proper connection. Another scenario could be that Godzilla mistakes the heroes for threats and attacks them. Then the heroes would have to combine their powers, like one hero creating a shield while another uses offensive magic, to fend off Godzilla's attacks.
There could be an ancient evil entity that has been awakened by Godzilla's presence. This entity wants to destroy everything in its path and sees Godzilla and Izuku as obstacles. It has the power to corrupt other creatures and turn them against our heroes, making it a very formidable antagonist.
One possible plot could be that Izuku, while on a training mission in an uninhabited area, stumbles upon Godzilla. At first, he's terrified but then realizes Godzilla doesn't seem to be immediately hostile. Izuku tries to communicate using his knowledge of quirks and signals. Godzilla, in turn, seems to recognize Izuku's heroic nature and they form an unlikely alliance to protect the area from a common threat, like a group of villains who want to use Godzilla's power for evil.
Kaiju novels often portray kaiju as gigantic and powerful beings. They are usually depicted as forces of nature that are difficult to control or defeat. For example, in 'Godzilla' novels, Godzilla is shown as a nearly indestructible creature with its atomic breath and massive size.
One popular 'kaiju x kaiju fanfic' story could be about Godzilla and Mothra forming an alliance in a unique way. Maybe they team up against a new, more powerful enemy that threatens their world.
The interaction would be complex. The heroes of Olympus have their own personalities and powers. Some might be afraid of Godzilla, while others would be more curious. For example, Leo, with his mechanical skills, might wonder if he could build something to either communicate with Godzilla or defend against it. On Godzilla's side, it doesn't have the same kind of intelligence as the demigods. It would respond to their presence based on its basic survival and territorial instincts. So there could be a lot of miscommunication and misunderstandings between the two groups at first.