Nice theory, I like it
Don't know if it'd be possible, reproduction compatibility wise (like cross-species or if the dark monsters even give birth like mammals, or by eggs like birds; what if monsters just form from energy, curses/magic, Frankenstein monster reanimated creation)
I can't remember if it was already ß said in-story
There are Divine beast (ML's clan), spiritual beast (MC, and other animal clans that are in the spirit realm), and malignant beasts (monsters). I think malignant beasts have a less chance to touch ML's power.
I went back to reread, ch2 is probably hinting that MC is half Divine beast - the vermilion bird(Kaizen)/firebird (Desire)/Nanjo (Myth)
I mainly read Myth Toon but that was such an awful line I had to check the others (╬ ̄皿 ̄)凸

So we all know that the mc is half bird and half unknown, and from what I understand is that there is beast spirits or whatever which is the animals and the monsters I forgot their names, what if the mc is half bird and half monster? And that was the reason his body didn't collapse or anything when he took ml power cuz he isn't normal he is half half, which makes me go to the another point where maybe the bird part parents has to mate with a monster since no one mates with their kind, maybe the bird part parents where desperate just like mc to have a child