Our Mc as you have probably assumed was indeed inside the blast radius, as a matter of fact, at the epicentre.
How did he survive?
Are mc was in charge of transporting chemical vials, now normally you would wear gloves whilst transporting toxic materials but the world had gone mad an honestly most governments wanted the rewards of technology even if it had a lot of risk, ie a hulk.
The chemical our mc was transporting was R.E.S, rapid evolution starter.
(Minor animal Gore/causality alert)
However it was still being fine tuned, cells would rapidly mutate and the weakst or worst mutations would collapse, animals however did not end nicely at all,52 rats had exploded in messy pools of blood and internal pieces. 3 Rabbits heads exploded, and the worst one was a puppy melting in goo whilst yelping it's lungs out. (You were warned).
At this point are mc was just about to load up the vials when a large shockwave jolted him causing the liquid to fall onto him. Before a reaction could occur the radition/ heat of the landing nukes hit him Turning him into an ash statue.
But this is the mc here, he is not just gonna die, a reaction occured and the heat and radiation caused him to rapidly mutate and crystallize forming an incrediblely hard substance capable of withstanding large kinetic impacts. In addition cells incrrased the production of melanin hence creating a protective layer and absorbing some of it to use as energy.
Then a nuke dropped near him burying him into liquefied rock.
(AN-You made all that up the readers shout and cry, typing insults in the comments, it's a story, so why not, just relax. Also some aren't, like the melanin thing as there are mushrooms in the reactor of Chernobyl that have a large amount of melenin)
Chaos was still present in the world and other than a brief mourning over the countries lost, the goverments scrambled all forces to take oil spots and salvage material.
Are mc at this point had regenerated most of his internal structure. However he looked like a rocky human, difference being the heart.
Since recovering our mc had become an organic reactor producing all sorts of elements, mainly hydrogen, which combined with the oxygen gathering inside of the body to create water hence producing a substance vital for the body, however it would not of lasted seconds if used as cooling. This was because this organic reactor continued to build in temperture, however the R.E.S that would have originally run out had started to increase and the heat and radiation acted as a catalyst causing it to grow in capacity and self replicate to the point that the heat was kept at an optimal level and the heart was the only organ affected by the heat and radiation, whilst the rest of the heat and radiation was consumed by the R.E.S to create slowly increasingly complex components.
Focusing on the surroundings, there was nothing but rubble, expected since it's an epicentre of a nuclear blast. However in the distance 6 black dots slowly approched. and got closer and closer.