Sanjay, I never like to discourage new writers, though I think that your friends are not giving you good advice. Their reviews really feel very stiff and awkward, like it was run through an AI. Nothing wrong with that, maybe they sit outside the mystery genre and are just here to support you.
That being said, I myself am a mystery reader, someone who works with AI closely, and a dramaturg first and foremost; my job is to teach and give the proper advice to new actresses!
So I will only give evaluation on the work that is presented to me, regardless of any preconceptions.
My core hypothesis is this:
Certain parts feel stiff. Descriptions of scenery especially feel very stiff and generic. Scenery is not core to the mystery genre, but it does set the mood. Here's the very first description:
Ravensbrook wasn’t the kind of city that demanded attention. It didn’t flash neon lights in your face or hum with the weight of history beneath cobblestone streets. No—Ravensbrook had a quiet pulse. A steady, subtle rhythm beneath its asphalt veins and glass-and-steel bones.
By day, it was a symphony of routine. Buses huffed at crowded stops, steam curling into the crisp air. Coffee shops overflowed with exhausted office workers, their eyes half-closed over lattes and stale pastries. The city was a chorus of conversations, car horns, and the occasional wail of an ambulance threading through the morning rush.
The lines are really long. Whenever there are long lines like this, especially in the second paragraph, my first instinct is to reword, and break it up. Why? Reader exhaustion! It feels like you are babbling and trying to get as many words out as possible. You do it for the dialogue and stream-of-consciousness in your writing, why not do the same for descriptions?
This is a common repetition in your writing style throughout the 1-4 parts I read. A trick to get around this might be this: when you have the image of the scene, break it down into components! Shuffle them around, gouging this scene through the heart with a stake, tearing those who are close apart, then marvel as a cackling golden witch appears in golden butterflies!
My second opinion is this:
Repetition is not suspense.
Sam's confusion keeps going on and on, and the main theme that is repeated in Chapter 1 is that he has a mark, but is confused. And he repeats the confusion three times...? Looping works in stories like RE:Zero, but you're just planting the same seed in a different garden!
My big problem is that it flatlines the story completely, the love plot goes nowhere, and weirdos start appearing like gangstalkers. But they don't do anything! Then we get Sam's confused reaction! Literally nothing happens except nobody can give him a straight answer! That's not suspense, that's just TV drama-style repetition...!
My suggestion is this: Make the seal important, like one of those lewd RPGMaker games. Your story reads very long for a first chapter already!
Webnovels do not work like the kind of publications Mr. Doyle wrote in. There needs to be punch in the storyline. 5000 works released just this month on a certain Chinese webnovel site this month alone. 2000 more in the last two days.
If the mystery meanders, that's okay. Its a pacing issue. Skill issue, easily fixable. Or its setting up something big. But if it repeats, with no great variation in tone, mystery, or urgency, I can't read on. I don't want to read on! Who knows how many more times Sam will keep going on about that seal! I want to read on but Mr. Sam is making it really really hard! The implication is very clear. If you don't understand, ask Simba what a 'lewd crest' is and how it is used in RPGMaker games. (laugh) We're seiso at House Delaroux! The mystery must progress, otherwise we are trapped in an endless recursion of summer!
My last opinion is this:
Violates mystery conventions
I'm not talking about the magic. That's okay. I'm the biggest Umineko fan on this site. I'm talking about the random characters that pop in and out of your story that are mysteriously (no pun) connected to the main plot. Not only that, they all uniformly point out the seal! At this moment I am thinking 'cultists'! But that's not right, because they magically disappear like a two-bit actor on a three-bit stage!
Knox the 6th: No accident must help the detective.
In your specific case, the reason I am against it in your mystery is that it makes Sam look really really stupid, that he can't solve the mystery on his own. Mystery readers want to root for the detective. They want to see the Furudo Erikas of the genre intellectually dominate the story! Otherwise, this is just a very slow shounen!
To your questions, my Final Answer is this: While the pacing needs work, and the characters are kind of flat, I want to be invested in Sam! He's just making it so hard because he keeps touching his seal and not doing anything 'mystery-related' about it! If the repetition was folded in tighter, given an uplift in urgency as Sam naturally panics at becoming more lewd (uwu) or whatever you have planned, it would read a lot better!