The Demon Sword Master of Excalibur Academy / Seiken Gakuin no Maken Tsukai
Plot Summary: One of the most powerful demon lords ever has been sealed away for a thousand years. When he finally awakens, he is reincarnated as a 10-year- old boy. Now under the care of the girl who released him, the demon lord Leonis must navigate the perils of Excalibur Academy.