Godzilla is an obvious choice. The dynamic between Mechagodzilla and Godzilla can create intense and exciting stories. Also, Mothra could be included. Her gentle nature could contrast with Mechagodzilla's more mechanical and often aggressive nature. Another character could be King Ghidorah. The three - headed monster could form an alliance or be in direct conflict with Mechagodzilla in a fanfic.
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.
Another theme is the search for identity. The female Mechagodzilla may be different from the traditional Mechagodzilla, and the fanfiction explores how she figures out who she is in the context of the kaiju world. She could be a hybrid of different technologies or have unique abilities that make her question her origin and purpose.
A Mechagodzilla x Mothra fanfic might explore their different natures. Mechagodzilla, being a man - made weapon of destruction, and Mothra, a symbol of nature and rebirth. The story could be set in a post - apocalyptic world where they have to work together to restore balance. Or perhaps it's a story of how their conflict shakes the very foundation of their world. There could be elements of human interference, like scientists trying to control Mechagodzilla while Mothra tries to protect the natural order.
A great 'kaiju x kaiju fanfic' should have a strong opening that grabs the reader's attention. You could start with a big battle scene or a mysterious event involving the kaiju. Then, develop the characters of the kaiju. Give them motives and desires. If you're writing about a lesser - known kaiju, introduce it in an interesting way. Throughout the story, build up the tension and drama. Whether it's a race against time to stop an evil kaiju or a struggle for power among the kaiju, keep the reader engaged with twists and turns. And don't forget to end the story in a satisfying way, whether it's a happy ending with the kaiju living in harmony or a bittersweet ending where one kaiju sacrifices itself for the greater good.
How about a Kaiju that can split into multiple smaller versions of itself? This would be a strategic advantage as the Jaegers would then have to deal with several threats at once. Each smaller Kaiju could have a different ability, such as one being able to spit acid and another being extremely fast.