A brief description of the manga The King Of Cave Will Live A Paradise Life:
Hiel, Prince of the kingdom of Sanfaris, was born with the unfortunate Cave King coat of arms.
Because of this coat of arms, his father, the King, elevated him to the position of Lord of a remote island.
Of course, there were no people, trees or plants there. It was an island with only one cave.
However, the moment Hiel, inside the cave, raised the pickaxe, the “Cave King’s” coat of arms activated. Its effect was to specialise in mining, allowing all kinds of ores to be extracted efficiently.
Among all that could be extracted on the island, there was one ore that increased your magic and even extended your life…
Hiell was so absorbed in mining that he eventually created the strongest country.