Okay, so the ultimate villain of my story is a million-year-plus-old malevolent extraterrestrial believed (and for good reason) to be the most powerful being in the universe. He has incredible strength, being able to exert a force roughly equivalent to 112 MN with just one of his fingers, and is quite morphologically similar to a human.
One of his favorite weapons to wield is a sword made of a space age metal that is about as long as he is tall (and he stands 2.25 m tall), has a mass of about 3 kg (swords tend to be surprisingly light), and has a cutting edge that is an atom thick at its thinnest, and gets macroscopic thickness that allows it to cause both physical and chemical damage to whatever it cuts. And it's got enough sturdiness to go through centuries of combat without having to be maintained. And, another ability of his wielder is firing lasers from his eyes that can heat a human being up to 3000 K.
I calculated the power of those rays by figuring out how much energy the victim would be losing to emission at that temperature, and those rays have a power that's equal to the power of emission. And that blade can cut diamond, as well as practically anything. So, how will it be possible for the wielder of the sword to cause a nuclear reaction by either splitting an atomic nucleus in two or by pushing one nucleus into another?