From what I could decipher from the hieroglyph : basically he can only stay by taking life force from our hulk. Which gets him stronger but also unstable.
But the whole Thing is that the universe Is literally rejecting his existence. Like he's a soul that has to pass away !!! So the universe Goes out to kill whoever tethers him in the living World
The black Haired ml is his anchor to the living ( ghostie guy feeds off his life force) and since ghostie guy can't pass away, it's having those evil repercussions on his surroundings, so it's the same as evil spirits : the more he stays anchored, the more stronger he gets as a ghost and the more he's dangerous and breaking balance.
So The world Sees an anomaly and is trying to get rid of it : which puts the black haired ML on it's hit list since he's the anchor of ghostie.(all those accidents)
That's why he begged the teacher Or Wtv to end him, cause he didn't wanna kill the black Haired ML. So nope our ghostie isn't evil as to say, he's just bigger than him.

Wait what, the last chapter is kinda confusing to me, what can make him stay?? His will to live? And how is that balanced out? I don’t get what they explained