fu** you bro wtf what was the point in typing that like why even have a chance of spoiling it like it maikes no sense like nobody wanted to know that or at least most us first time readers jesus
What really happend was that after killing andares the monarch of destruction he used the cup of something for the last time to rewind time 10 years undoing everything amd took on the whole war himself spanning 20 years as he killed all the monarchs again and there was many forshadowing to him doing this like the fortune teller saying that he was going to bear everything himself with him saying thank g** i make it in time. After words since time flowed differently so it being 20 years for him it was like not even that long for everyone else so he went back to his middle schooler body and lived a normal life with the last scene being him and cha hae-in his potential love interest staring at eachother before it ends.