Wise Man's Grandchild

Wise Man's Grandchild (also known as Kenja no Mago) is a classic isekai fantasy anime.

A young Japanese salaryman dies in a car accident and is reincarnated as a baby in a magical world filled with demons and sorcery. He's discovered as an orphan infant after a demon attack and adopted by the legendary hero and powerful sage Merlin Wolford, who names him Shin Wolford and raises him as his grandson.

Merlin (and his wife Melinda) train Shin intensely in magic, combat, and enchanting from a young age, turning him into an overwhelmingly powerful prodigy who far surpasses normal mages. However, because Shin grew up isolated in the forest with only his grandparents, Merlin realizes on Shin's 15th birthday that he completely forgot to teach him basic common sense or how normal society works.

To fix this, the king of the Earlshide Kingdom suggests Shin enroll in the capital's prestigious Magic Academy. There, Shin meets new friends (including a love interest), rescues people with his OP abilities, forms a club, and navigates school life, battles, and social situations—often hilariously misunderstanding "normal" things due to his sheltered upbringing.