I finally have my concept ready haha. Been a while but here goes:
It'll will be a trilogy and will revolve around the extermination of Godzilla himself. I dont want to use any other monsters here as I have a different ideal approach.
My ideal composer for this would be: Hiroyuki Sawano. His ability to enhance any emotion in a scene with ease makes his talent eye-catching.
Film 1: In summary, this film will have Godzilla make his debut to humankind with the intent to destroy. I want to not only show how cruel and menacing his existence can be, but the horrifying effects of his iconic breath. Imagine if Godzilla's breath attack on a human being not only vaporizes them, but leaves an atomic shadow of them? The film's primary focus is to show the terror of something like Big G attacking mankind and the aftermath of his rampage, while also solidifying humanity as the underdog of this trilogy. Godzilla will evolve his abilities slowly, allowing him to get to his peak by the third film.
Film 2: This film will focus on preparing humanity's comeback, with the drive to fight back against this threat. Godzilla is claiming the world as his territory, and humanity is losing its edge. They realize that if Godzilla is evolving, they also would need to push forward and advance their tech and weaponry. They begin to develop a counter-offensive, a fighter of their own. Something to withstand Godzilla's abilities but realistically still be prone to damage by them (the film wouldnt be fun if it could just tank what Godzilla throws at him).
Film 3: This film is the endgame. The final offensive against Godzilla. The mech has been prepared, but Godzilla has already turned a good amount of larger civilizations into a azure-scorched wasteland. This film represents humanity's comeback, with humankind banding together to stop a common enemy as a species. Since this would be all-out war, this film would have countless casualties. The tone still being consistent throughout as a horror with realistic, yet bombastic action. The mech's purpose is to damage Godzilla enough so we can deal the final blow. Hoping the mech kills Godzilla by itself is wishful thinking and would be cliche plot-wise.
This is just a summary but I'd love to go in-depth with this in a legitimate topic. The whole point of this trilogy is to introduce the audience a horror trilogy with an iconic monster while also holding out hope that humanity will survive and triumph against him. Godzilla started off as a horror film, and I believe that using that tone not only does him justice but shows audiences what he was before he was a hero. He was a towering horror, and he still retains his badassery that way.
(I did have a secondary concept that revolved around a "Destroy all Monsters" with Ghidorah being the cosmic threat against the world. I feel he isnt properly conveyed to be such and I think having him be the unholy destroyer could be a pretty dope thing to see on-screen.