Tensei Shichattayo (Iya, Gomen)(Um, Sorry) I've Been Reincarnated! ; Я был перерождён! (М-м, Прости) ; 一不小心转生了 ; 転生しちゃったよ（いや、ごめん） ; 미안, 전생 해버렸어

From MangaHelpers: After a god screws up and accidentally takes high schooler Shou's life, he offers him reincarnation with a gift to make up for it. Shou asks to retain all his old memories for the new life. Shou is reborn as Will, a noble's son in a world where magic use is common and involves knowledge of kanji characters. With all his memories, he's a brilliant toddler, and when he experiments with magic, he finds that he has an amazing talent for it! What's more, though he was smart but unloved in his old life, in his new life he has a mother and a father who both love him deeply. His future as Will is looking very bright!