From the age of four, when his parents died, he studied ancient martial arts under his grandfather, a Living National Treasure. While remaining in Japan, he learned techniques for combat and killing.

One day, as he was about to graduate high school, he became caught up in an inhumane spell that "forcibly summons and enslaves people from another world."

What he saw next was not another world—but his parents, who should have been dead.

His parents, who had been watching over him as guardian spirits even after their deaths, though they couldn't prevent his transfer to another world, succeeded in rewriting only the "enslavement" part into a different power.

The powers they bestowed upon him were a game-like menu function, designed with his mother's full hobby-driven enthusiasm, and a skill from his father, tailored for his son who excels at learning by observation: "the ability to copy any skill he sees once and make it his own."

※This is a typical 'isekai (another world transfer)' story, where the protagonist is the strongest, and features a 'learning/copying' system.

Harem elements included.

※Retitled from 'When I Went to Another World, I Gained the Ability to Copy Skills'.