Around 40 Kenja no Isekai Seikatsu Nikki: Kimama na Isekai Kyoushi Life

A middle aged man reincarnates in another world and becomes the strongest tutor in the world! Satoshi Osako (40), who had become addicted to the game and rose to become a top player, had an accident while logging in that put an end to his life. In a world full of swords, magic, and monsters, he was reborn with all previous statuses and somehow ends up tutoring a young girl... The diary of a wise man who lives in a different world, where his motto is "Peace and tranquility every day." (Source: Square Enix)