The beginning of the story was hella confusing! Like how did he figured out that he can use his mirror to enter the murim world? Tho if you look at it carefully, you could understand it. Well, although the MC kinda always used his feelings to the decisions he make, this series is kinds good. The art is good too.
So, He goes inside the mirror, then saw the former demon blood leader then he was recognized as his successor, then he go back to the modern world and be a normal student again.
Before his exam, he enter the mirror so he can use the stopped time to study the exam but was found by the elder of the blood demon subordinate and bring him back to the headquarters to become their leader and then bam. The story start.
Devil Sword King