Boi

After 2000 years have passed, the ruthless demon lord and his partner/brother has just been reincarnated! But they aptitude at an academy for nurturing candidates for demon lords is, "inept"!? Having the capability to destroy humans, elementals, and gods, after a long period of countless wars and strife, Arnos the demon lord became sick and tired of all that and longed for a peaceful world, so he decided to reincarnate to the future. However, what awaited him after his reincarnation is a world too used to peace that his descendants became too weak due to a huge weakening in magical powers.

(Yeah I copy paste the description of the anime)