Well, it really depends on various factors. Mega Man has his wide array of weapon upgrades and his ability to adapt quickly in combat situations. Astro Boy, on the other hand, has superhuman strength, flight, and some really advanced built - in weapons. If it's a long - range battle, Mega Man might have the upper hand with his precise shooting skills. But in close - quarters combat, Astro Boy's strength could overpower Mega Man. However, if Mega Man manages to analyze Astro Boy's weaknesses during the fight, he could potentially turn the tables.
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.
One interesting plot twist could be that Mega Man and Astro Boy end up teaming up instead of fighting. Maybe they realize they have a common enemy that is threatening both of their worlds. Another plot twist could be that Astro Boy discovers he has a hidden ability that makes him immune to Mega Man's weapons, which completely changes the dynamic of their fight. Or perhaps Mega Man gets corrupted by some outside force and Astro Boy has to find a way to save him and bring him back to his normal self.
Some fanfictions explore the idea of the two Pokemon learning from each other. After the battle, whether it's a win, lose or draw, they might exchange some sort of knowledge or experience. Maybe Greninja learns how to be more aggressive from Charizard X, or Charizard X learns about agility from Greninja. There are also plotlines where the battle is a test of friendship or loyalty between the Pokemon and their trainers.
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.
To write a compelling Kaiju character, start by giving it a distinct appearance. Describe its size, color, and any unique features like spikes or tentacles. For example, a Kaiju with a massive, spiked shell on its back is immediately more interesting.