
Beautiful art, fascinating plot. A little weird that the past is in white and the black is in present, but I think thats just for overall tonality and mood.
Anyway. I've been thinking it was Jun from the beginning, but I'm kind of all over the place with this. I don't have a clue, but I have a feeling it might be the pretty boy interpreter, or maybe it really was Inu himself and we're all being lead around by the nose.....

No one but Hyeol is showing yandere traits, and those are shallow at best. Lol.
But, omg! Is Our Sunny Days coming back?! Seeing the baby at the end made me really miss that manga....
Anyway! That was one creepy stalker. I hope it doesn't turn into anything serious and is instead something comical....like a coworker waiting for SH to come back to work due to overload or something...

I feel like Dan's grandma is gonna die, he's gonna get an offer from a reputable place that will pay off his debt to JH and he'll go to tell JH that he's quitting, but he'll have already found out. JH will get pissed and Dan will tell him he already has a place lined up but will send for his grandma's cabinets. JH will yell about how he's done so much for Dan and Dan hasn't done anything even close to the same so they're not even. Dan might actually stand up for himself, but JH will get pissed and starts destroying the cabinets. Dan will try to stop him, but JH will be seeing red and not even noticing what he's doing. One of two things will happen then; 1) The cabinets will be destroyed and Dan will be so devastated that even JH will notice and Dan will leave angrily, bawling. Or 2) one of the cabinets will start to fall and Dan being Dan, will shove JH out of the way and get trapped under it and severely hurt. In which case, JH might actually say his name, which he's never done. (They've also never kissed, either...)
I have a bad feeling that all of that won't take place before another rape. I have a bad hunch that the hospital will be calling during it and JH won't let him answer the phone and Dan will miss out on being able to say goodbye to his grandma. . . . . Yeah. Seems to fit this story. I don't think JH can be redeemed at this point. Normally, I won't give up on MLs, knowing that every person can change if they want to. But JH seems to like being miserable and angry all the time. He's selfish beyond reason and has such a short fuse that I don't know what it would take to get him to realize he has to change. Unfortunately, I think Dan getting hurt for his sake after he's been nothing but an asshole will be the only thing that does it. Just a theory though.

As a Duke, even a Grand Duke, he should be referred to as "Your Grace", not "Your Highness". It has bothered me this whole time. Lol.
Cute story. Funny, light and interesting.

Disclaimer, I'm gonna info dump:
Most of the Grand Duchies and Archduchies are given because of them being related towards the royal and imperial family and/or they did something honorable/worth of merit, and sometimes, they're even regarded as someone on the same status as the royal and imperial family themselves with the perks of the same status, hence they even retain getting addressed to as "Your Highness" and such...
Hence though Alexis might be a Grand Duke and must be addressed as "Your Grace" like the other european monarchies, I think "Your Highness" is still fitting.
Plus in other european monarchy, the ruling houses are grand duchies and archduchies and uses "Your Majesty" and "Your Highness" to address monarchs and their children, so maybe the author made a reference towards those?

Actually, those referred to as "Your Highness" that are grand dukes or duchesses are only those related to the royal family. While this can vary from country to country, in general terms, when dealing with natural hierarchies in fictional or fantastical settings, grand dukes are referred to as "Your Grace". As our ML is not related to the the royal family by blood or marriage and was gifted his title, it is wholly inappropriate for him to be called "Your Highness", as this is meant to show distinction between those who carry royal blood and those who do not.
The translations go from being good, then to lazy and then to bad, and back to good again. Whats up with this??