I'm not going to spoil a thing for you because ;).... but go back to the beginning and read the panels and the scenery right around when Jaewon drops the book. Then FF to the day the Jaewon and Dojoon have sex. Look at what he says, the words he says are verbatim to the novel so no typos. To the truth of the word of the story calling him a regressor is inaccurate. Focus on Jaewon. The season is about to wrap up, so your question wont be answered just yet given the break its on but if it makes you feel better you'll know by like chapter 2 of the next season. The spoilers that have been dropped aren't malicious though
I read some spoilers online about the novel. No one talked about Dojoon being a regressor tbh
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//major spoiler alert about the plot//
It looks like Jaewon didn't trasmigrate either. He went back in the past (thats the reason behind those old phones ig), around 13 years earlier. Then he got into an accident and got back to his time. Meanwhile, during those years, Dojoon searched for him. Kinda guessed but it was him who gave Jae the book right before his first accident
So basically, if I dont remember properly, SOMEONE in thid comment section, told me dojoon was a regressor can someone tell me if its it false info because it kinda seems true, or im I gullible