Return of the 8th class Magician is a Manga/Manhwa/Manhua in (English/Raw) language, Manhwa series, english chapters have been translated and you can read them here.
The Summary is
It’s been many years since I’ve bloodied my hands for the United Empire and it’s emperor, Ragnar. I wanted to return to my home town and live a quiet life as if to repent for my sins.
“You are a great 8th class magician who is able to overthrow me and the empire at any time”
“How could I let a monster like you stay alive?”
After being betrayed on the verge of death by Ragnar, who was my friend as well as my Emperor, He stabbed my heart with a dagger that had time magic applied to it.
“The redemption I want, is to put everything back to its place.”