Kenjutsu Meika no Shitsuji wa Eiyuuou Datta

Crowley, the Hero Emperor, was humanity’s strongest warrior—a conqueror of demons who attained eternal youth from the fruit of the World Tree. Yet at the pinnacle of his glory, he was struck down by his closest friend, the Archmage Raphael. Two hundred years later, he awakens reincarnated as Faris, an enslaved youth serving a ducal house. To his shock, rumors declare that the Hero Emperor never truly perished, but still battles demons at the World Tree as a hollow husk. Determined to uncover why he was betrayed and what remains of his former body, Faris breaks free of his chains by striking a deal with the ducal family: become the butler and swordsmanship tutor to Rimuru, an incompetent young noblewoman, and mold her into the rightful heir. To reach the World Tree once more and unearth the truth of that fateful betrayal, the legendary emperor embarks on a new ascent. Original Webtoon