Gomi Ika da to Tsuihou Sareta Shiyounin, Jitsu wa Zense Kenja desu ~Shijou Saikyou no Kenja, Sekai Saikouhou no Gakuen ni Kayou~

Gard has devoted his days to serving a count's family, only to have his loyalty repaid with betrayal. Falsely accused of a crime he never committed, he is dismissed on the spot and branded as something even lower than trash. Cast out of the estate with nothing to his name, he finds himself alone on the streets with no home, no reputation, and no prospects for the future. While drifting without direction, Gard comes across a flyer announcing student recruitment for the Remillion Magic Academy, located in the royal capital. The academy's entrance examination is said to be the most brutally difficult of any magic academy, a barrier that few applicants ever manage to overcome. Undeterred, Gard resolves to take the test—and passes it with effortless ease, an outcome that defies all logic for someone who was, until recently, a mere servant. The secret behind his astonishing success reaches back beyond this lifetime: in his previous incarnation, Gard was none other than the strongest sage. Now, armed with the wisdom and power of history's greatest magic user, the once-condemned servant steps into a remarkable new life at the world's most prestigious academy.