Kenja no Mago Manga Series by Tsuyoshi Yoshioka

A young man who had surely died in an accident, was reborn in another world as a baby! After that, he was picked up by the patriot hero "Magi" Merlin Wolford and was given the name Shin. He was raised as a grandson by Merlin and soaked up Merlin's teachings earning him some shocking power however, when he became 15 his grandfather Merlin said: "I forgot to teach him common sense".

Adapted From Kenja no Mago (Novel) - Magi's Grandson (Novel) - Philosopher's Grandson Original Web Novel Associated Names 賢者の孫, 賢者之孫, 현자의 손자, Magi's Grandson高等魔法学院に入学した“賢者の孫”シンは、同じく入学してきたシシリー達と再会を果たす。クラスメイトと親睦を深める一方で、静かにだが確実に魔の手がシンへと迫っていた…。 Thanks to various magic, the human race has been saved from calamity many, many times. Retaining his memories from his previous life, a boy, Shin, was brought up by an old man known to the world as the "Magi" as his grandson... moreAdapted From Kenja no Mago (Novel) - Magi's Grandson (Novel) - Philosopher's Grandson Original Web Novel Associated Names 賢者の孫, 賢者之孫, 현자의 손자, Magi's Grandson高等魔法学院に入学した“賢者の孫”シンは、同じく入学してきたシシリー達と再会を果たす。クラスメイトと親睦を深める一方で、静かにだが確実に魔の手がシンへと迫っていた…。 Thanks to various magic, the human race has been saved from calamity many, many times. Retaining his memories from his previous life, a boy, Shin, was brought up by an old man known to the world as the "Magi" as his grandson. With the memories of his past life, he absorbed the Magi's craft and grew to be able to develop his own magic.Then, the grandfather told him he has to become independent when he reaches the age of 15."Ah, I forgot to teach him common sense."The grandson who has grown beyond the level of normal people, lacked common sense; the common sense of the world. So to learn how to socialize, he went to Earlshide Kingdom City to go to Earlshide Advanced Magic Academy. Where he will reunite with Sicily, who has also entered the school. While deepening friendships with classmates, quietly but surely the hand of the devil was imminent to Shin.... less

{Chapters 8-11}Shin defeated Kurt his classmate who had turned into a demon. He is now thought of as a hero just like his grandparents. His popularity at the academy is terrific, and the people who wants to join the "Ultimate Magic Research Group" that Shin sponsored is flooded. Everything seems to be smoothly, but is the threat over...