[@Lmpkio] If it helps the concept, I could have him start out in a dying/weakened state, with his nuclear heart weakened and unable to generate a lot of power.

I also had a concept for him to have a humanoid form, perhaps he begins that way and is eventually able to restore his full dragon form? I think it would fit in with the "last of his kind" narrative I'm shooting for. As a "human" he'd be less nuclear devestation, and more weird space magic. I think it would be funny for something roughly human-sized to go toe to toe with the big monsters.

Up to you.