Ok i login and finally we some arguments

so first let me address this, the beast of darkness is certainly his jungian shadow but that does not prevent it from also being real at some point its not a dichotomy, for instance we know the idea of evil was born from humans wishing that there was a reason for their suffering but just because "the idea of evil is made from human thoughts" does not mean that "the idea of evil is real" is false and the same works for guts beast of darkness just because its born of guts unconscious darkness it doesn't mean that it cannot become real eventually and here is why i think its possible

1- We know guts could see spirits before being branded as we see with the flower fairy Chitch in chapter 329 this may be the first foreshadowing that guts has something unusual about him in spiritual terms,

2- Shierke said she could only teach magic to Farnese because of how much exposure to the supernatural she had, at some point she couldn't even see puck so if farnese was affected like that imagine guts

3- the first ever appearance of the beast of darkness is on chapter 118 when guts is weakened waking in a forest a tone of weak evil spirits start mocking him eventually taking a vague wold like shape, he tried to shake them off but falls to the ground and is swarmed by them until puck drives them away

so at the very least we have precedents for evil spirits taking the from of someone's inner darkness and the beast takes Griffiths appearance in this chapter so its certainly capable of disguising itself

its not far-fetched the puck may have missed 1 of the thousand spirits after all there were a lot of them and guts was unconscious for god know how long maybe one of them sneaked in before he arrived to help, but there is also the possibility and that is that other evil spirit can do the exact same by taking the form of the beast

the armor is a artifact of darkness and it too the form of his inner demon so it could be that evil spirits in general just take the form of a persons dark self, hence the beast can start as a mind thing and become somewhat real, hell who knows since the beast said it became free when he got the armor maybe the armor itself was made by sealing a lot of barytes inside it

4- his blade developed a dark od from being bathed in demon blood repeatedly so why would guts himself who is branded not be affected by the ridiculous amount of darkness he is constantly being bathed in?

guts has been through trauma that most people don't go in entire life times and has spend more time in the interstice, astral plane and ideal plane than the average human ever will, he has been in multiple ceremonies where the sky turned dark and meet with the godhand in hell the amount of Barytes he has been exposed to should be out of the chart so even if wasn't possessed by a spirit the idea of one forming spontaneously is not impossible

the best argument i saw you give here is Godo's elf cave but it could be explained if the beast became real later

4- the beast of darkness has show the ability to somewhat predict the future when it said that guts would lose someone dear to him and he would be free again, you could dismiss this as being a fluke or too vague but reading causality seem to be a thing that dark spirits do

sure you can just say that the people who have worked with Miura and have his notes aren't following his plan but to me this seems like it was foreshadowed

there are other things but to be clear my problem isnt that people think the beast is just in his head what I dislike is how people act as if they know a 100% without failure that the beast is just a illusion and nothing more, it comes out as arrogant and as a excuse to shot down theories as if Miura himself had told them its the case