Finally!

Im still confused plx explain to me bestie ╮(￣▽￣)╭

HAHAHAH omg which part?

Frfr bestie preach (｡•ᴗ-)✧

From the start everything ┗( T﹏T )┛

⁄(⁄ ⁄·⁄ω⁄·⁄ ⁄)⁄

Omg hahahaha it's gonna be a long ride but I'm telling you this first that this is just how I understand it my own okay? So it's not really precise or anything XD..
So I did a quick run from the ch.1 and now I can kinda understand it better.

So in the begging where it all started is when giyoon saw the ghost director masturbating in jumins desk, yes it's the ghost and also there are multiple ghost in this story not just the ghost director.
That's why when giyoon got cought by the D.Ghost (director ghost) he ask giyoon if it's yitae(the real director) who his seeing and how he got involved in this, because the ghost is only pestering jumin and now an unexpected person kinda show up which is giyoon ( I think giyoon has the ability to see ghost that must be why)
So the one masturbating is the D.ghost okay?
Then the next morning it was the R.director (real director) not the ghost anymore.

Nxt.... Is when he did an overtime with the R.director and there was a power outage or something then the R. Director went to check the electricity leaving giyoon alone in the office.
Then the director came back, but no it was the ghost.D. and he did those horrible things to giyoon, and the guy in the elevator too that giyoon saw is also a ghost.

Now in the conference room where the girl saw the ghost. Yes it was the ghost director of course hahaha

Nxt is in giyoon's house, some got confused if it's the real director or not.... But no it's was the D.Ghost who's in giyoon's house in was the ghost.

And in the recent ch. When they're at work and the director just got back on his business trip, yes it's the R.director who's in there and the one who kissed giyoon and ask him to meet at the evening, it was the real director okay?
But in this last chapter when giyoon was over timing again and got a call to go in that room, it was the D.ghost who kissed him this time and was pissed off by the fact that giyoon let the real director kissed him and he did not resist at all but when it was the D.ghost who kissed him he keep resisting and that's also why the ghost director realize that maybe giyoon is only pretending to not know about the ghost.

Just remember that if the director looks scary looking and talk nonsense with giyoon like about sexual stuff and such, it is the ghost.D

Also have you noticed that the real director always has a little reaction from the start everytime he saw giyoon having a bruise on his mouth and also when he got sick, then despite their not so good relationship, the director is kinda being considerate of giyoon specially that time when he accidentally splash him with his drinks, and also the words that the director said to giyoon in the stairs proves that the director knows about the ghost and stuff, is aware of what's happening to the both of them.

That's because from the very start the real director is aware of it all, as the ghost is using his body not really his real body but just the appearance, he's aware of what the ghost is doing whenever the ghost has its appearance, through a dream or nightmare, so yeah the real director is asleep as will as giyoon, that's why everytime giyoon face the D.ghost he soon will wake up like he had a horrible nightmare but it feels too real as his body can remember and has traces of everything that happened between the ghost.

And as for why giyoon seems like his kinda dumb for not realizing that he's facing a ghost despite it being obvious is probably because...
Based on what I've seen from other comments
Giyoon is probably pretending that he doesn't know anything about the ghost, because if you acknowledge their presence they will hunt you even more or if the ghost knew and realized that you acknowledge their presence, that will only excite them and never leave you alone and probably break you or something....
Remember the girl who can see those ghost? And acknowledge their presence and even talk to them coz she couldn't take it anymore? Something happened to her right? when she was in that room and we don't know what happened to her next.
So that's kinda it somehow hahahaha(￣∇￣")
Hope you understand ʕ´• ᴥ•`ʔ
THIS IS ONLY BASE ON MY STUPID LITTLE BRAIN SO ITS NOT RELIABLE.¯_༼ ಥ ‿ ಥ ༽_/¯

I'm not sure if you can understand this explanation hahahah .

Also jumin is sus too hahahah and giyoon and the ghost is maybe related to each other way back in the past because of that one chapter where giyoon dreamed of the ghost and I think he called out the ghost name while asleep that's why the ghost was in a good mood when he was lying and looking to giyoon (in giyoon's house)

Wao i had no idea now i kinda grasp the plot thanks