(Spoiler alert: if you haven't read far into the webtoon yet I suggest you read the story first)
Relationship headcannons cause I couldn't resist writing it
When you first met him he came off as crazy (he is)
When you first saw him rip out a guy's throat to get the ball (first test on blood corpse valley) he got your attention, by terrifying you (hey something's still better than nothing right?)
You first got his attention when he noticed you could see the demons around him, or at least sense them somewhat
Not gonna lie, at first he planned to kill you like he planned for everyone else (death qi requirements and all that, he's a hungry boi) but when he noticed your peculiar ability he decided he could use a sidekick of sorts
Definitely leaves you behind to do his work or take the attention off of him when he's off on his little side quests (que killing more people or finding new ways to kill more people and eat their energy)
One of your greatest nightmares in your days of covering for him would definitely be washing his clothes, you swore you washed that pair just yesterday and he's handing it back covered in blood like what? Chill bro (poor you, can't even say no cause the guy's terrifying)
He definitely enjoys scaring you, you can't convince me otherwise. It's that little crack of a smirk on the side of his lips every time your eyes widen a little in terror that you overstepped boundaries and might be killed.
He has decided to not kill you yet, no you're still useful to him. That doesn't mean he doesn't threaten to do so in order to keep you in line and you believe him every time since you're not going to try and find out what happens if you protest.
OK, that's as good as you can expect it to be between you two on the first days of your little 'agreement'. You listen to him and in turn he doesn't kill you (you may even benefit from helping him due to his growing position in Cheonji, he says). But what happens after a few more weeks you ask?
Gyeong has begun to trust you more, enough to tell you his name (you think it's Gyeong cause he still hasn't given you his real name, he doesn't plan to)
But hey despite everything you have to endure from him you can rest assured he'll make sure you have no other problems at Cheonji
The difficult tests and missions? He's found a way out for both of you. Your overly murderous peers? He's killed them all
You hate to admit it but having him as a 'friend' is actually pretty useful here at a place like Cheonji where there's no certainty whether you'd live tomorrow. That is, if you're not following him, if you are then good news for you. There's no way you'd die as long as he still has use for you
You don't know how to look at this arrangement, there's no way in hell you're friends and there's almost no difference in your ranks (he pulled you up the ranks with him) for you to be his subordinate but for now he provides as good an assurance for survival as you can get
However none of these things change the fact that you're a subordinate in all but name to him. You help him with his qi circulation and daily necessities, you follow his plans and sometimes even aid in making them
But there's still a boundary between you two, you've been through life threatening situations where you had no choice but to trust in his judgement. You two have been through situations that could bring total strangers close but he doesn't seem to care about that
Death and risk comes so naturally to him that he enjoys it, you know that fact and sometimes can't help but feel thankful for how talented he is but that same fact is what makes those situations somewhat mundane to him
It's not because he's suspicious of you, he just doesn't get what's so great about surviving something together. To him you'd still be a subordinate in all but name even if you've known each other for months
At this point, something major has to happen for him to see you any differently. Maybe you helped him out of a hopeless situation (highly unlikely), maybe you sacrificed your life for him or maybe you got him a high level grudge for his collection
He doesn't understand why you'd put yourself in actual danger for him, seemingly without wanting anything in return. This is when your.....partnership turns to something more
He no longer threatens you if you protest, doesn't scare or blackmail you for a few mistakes, he even let's you back out of things simply because you didn't want to do it
He's come to respect you as a friend, maybe even a partner if it gets there. People that try to kill you are never heard from again. He's already lost almost everyone who cared for him, he refused to loose you too
Your interactions got considerably lighter, he'd even crack jokes and laugh at yours. Sometimes he'd act in such a way that you couldn't help but think he's almost fond of you
He's become more accommodating of your moods and more attentive towards you in general. He even teases you sometimes and leaves a few gifts
Your spiritual power has grown weak? Demon sage left a few healing talismans and spells for that. You were trying to learn a new sword formation? You see demon sage sneaking in the corner of your room to deliver scrolls with in detail explanations
He even has demon sage keep an eye on you to take notice of the things you like (The grudge is instructed to not be seen by you but you spot him anyway)
On a hard day you might find your favorite candy on your bed and you know exactly who it's from
Gyeong even invites you to take late night walks with him in the grounds or the forests around Cheonji, he insists it's because patrolling together is more efficient but that's only because he has no idea how to ask you out on a date
I don't see him being too emotionally supportive or even into things like PDA, acts of service is by far the only way of showing affection that he's comfortable with
So that's it for now, I might add NSFW materials in future posts. I'd like to hear your opinions on this