#1 - Bloating of backstory. This is supposedly isekai, though the 'otherworldly' aspect is insanely limited, and I am willing to say at this point - inconsequential; A guy from our world got thrown into, what wants to be, a cutthroat quasi-medieval world. ENTIRETY of 'otherworldy' elements is backstory, it has no impact at all on character; Characters acts as an in-world inhabitant would, and after removal of that aspect nothing in the story would change. The character adopted to the world LITERALLY within minutes at worst.
#2 - Inconsistency - Could author please decide, whether or not the 'kill aura' even exists, and if it does is it a problem or not? The 'problem' was fixed literally within minutes of meeting someone else; 'Magic beats', true but still [btw: Except for exotic animals, no animal was shown to be of any intelligence above what you would expect from a lizard or a bird, so having suddenly magic beats is an AFREDS in itself]. Only when plot demanded ANY intelligence of interest is shown, in exactly the scope it needed - a single beast.
Also - is that beast strong to remove a 'kill aura' or can anyone do that? If the latter - why the hell isn't it common? Also - why revenge killing makes you marked but apparently - working in a military, or in 'shady business' has no impact on it whatsoever. A coup? No problem; Killing of killers? Now you've done it.
Another example - In later chapters royalty orders the family to 'release MC from servitude and adopt it', later on point is made that one character is thinking about relationship with MC, as if it changed at all, and another example shows that the MC was actually adopted into family...
In practice however he is still bound by a servitude contract [which has another issue, about that shortly], so why is there a difference in relation expected? The LACK of removal of servitude is hidden from the reader, implying otherwise, only to use a shock value of the 'tragedy'.
Barriers - Could author please decide what these supposed barriers can and cannot do? Apparently they can block and manipulate air inside, but cannot protect from burning, apparently they are good enough to keep family treasures [supposedly even royal treasures], but can be bypassed by as much as WALKING THROUGH THEM even if you have no permission.
On a side note - It felt like the martial abuse backstory was shoehorned in for the 'pity' points alone, as frankly - despite being told about it the effects on the character were extremely limited, to the point of teasing of MC in ways that I would be willing to bet a martial abuse victim of that type would not even think of as being 'funny'.
#3 - Insane degree of stupidity of characters.
Let me ask you two questions:
Situation - You live in a cutthroat world, where even relatively good guys make insane demands, probably to find a hook on you AND the danger is so high that you are specifically looking for 'barier master'.
Question - Why in the hell's name would you allow 3rd party [not the guardian and you] to have ANY control over that guard?
You have even given the guard access to family treasury AND adopted him into family. Why in the hell's name would you allow anyone else to have any degree of control to them, especially someone in business of human trafficking?
If you answer 'because he's a slave, and slavery is normal' then tell me - will you give someone your banking details? Will you give for example a bank clerk your internet banking login, password and 2FA data?
No?
Why not? they have access to banking system anyway.
#4 - buildup and use of tragedy
Entire buildup comes from a single mention 'yeah, we'll F him up', until the actual S hits the fan. Aforementioned logical [in-world] and inconsistent elements are used in order to deliver shock value, frankly similarily to overglorified [regarding tragedy aspect, in my opinion] Martin's series. Edit: in hindsight - in Martin's work there's much more buildup, but still tragedy elements are largely introduced for shock value.