Mergin was summoned thousands of years ago as a support member of the hero party to defeat the Demon King. Mergin possessed magical power and aptitude to the extent of being called a great sage, and about ten years after being summoned, he headed towards the Demon King’s subjugation as a member of the hero party.
However, immediately after Mergin, who was a support member, shot through the Demon King’s core, he was petrified by his comrades. The petrification was not lifted until thousands of years later.
And thus, Mergin began a new life in the world thousands of years later.