The Math and Science Mage

An internet operations specialist transmigrates to a world of mages, made up of oceans and islands.

He decides to study magic scientifically, with a few dreams in mind: making a hydrogen bomb with his bare hands, creating a hundred-million-degree blast bomb, and finding his way home.

Without any cheats, he keeps growing stronger while constantly recovering from injuries, or getting injured on the way to recovering.

As for a heroine, she would only slow down his bomb-making.