Toki Tsukai Majutsushi no Tensei Musou: Majutsu Gakuin no Rettousei, Jitsu wa Saikyou no Jikankei Majutsushi Deshita

Arvis is a poor, low-achieving student at a remote magic school. One day, he was given the impossible task of defeating the smartest student in his school, or else he will be expelled. Arvis looks after his little sister who's blind and frail, and depends on the scholarship from the school to survive, so he started training as hard as he could! Not only did he not acomplish anything, he passed out from pushing himself too far. But then, he had a mysterious dream. In the dream, he was a legendary mage in his previous life, and was using the now extinct time magic to make quick work of demons! When Arvis woke up from the dream, he had the ability to use the legendary time magic?! (Source: Manga UP!)