It could start with a strange energy wave that pulls Godzilla into the Rosario Vampire world. The first to notice could be Tsukune and his friends, who are initially terrified but then realize they need to do something about this unexpected visitor.
It could be about Godzilla emerging in the world of Evangelion. Maybe the Angels in Evangelion are confused by this new giant monster. The Eva pilots might have to deal with both Angels and Godzilla at the same time.
A possible plot could be that Godzilla is accidentally teleported into the Pokemon world. The Pokemon trainers think he is a new, extremely powerful and dangerous 'Pokemon'. So they try to stop him. But as they try to fight Godzilla, they realize that their normal attacks have little to no effect. Then, a group of legendary Pokemon, such as Arceus and Lugia, decide to communicate with Godzilla. They find out that Godzilla is just as confused as they are about this new world. Together, they try to find a way to send Godzilla back to his own world while also dealing with the chaos that his presence has caused in the Pokemon world, like disrupted ecosystems and panicked Pokemon.
No, the 1954 Godzilla movie was one of Godzilla's earliest works, but it was not the earliest. The name Godzilla first appeared in a Japanese manga of the same name in 1942. Before that, there were other forms of Godzilla's image, such as appearing in news reports, posters, and advertisements.
If RWBY were to watch Godzilla fanfiction, Ruby would likely be the most enthusiastic. Since she has a love for adventure and heroic tales, she'd be quickly drawn into the story. Weiss would initially be skeptical but could get into it if the story had a well - structured plot. Blake might see parallels between the power dynamics in the fanfiction and those in her own world. Yang would just enjoy the chaos and destruction that Godzilla often brings in the stories, finding it thrilling.
In this fanfiction, Harry might have a unique form of magic due to his Godzilla lineage. Instead of using a wand in the traditional way, he could use his roar (like Godzilla) to cast spells. His enemies would be really confused by this new form of magic. And his relationship with Dumbledore could be different too. Dumbledore might be more cautious about Harry because of his unpredictable and powerful nature.