Responses
im not sure about this but only the Uke can heal him just like the first time he died, they fuck like rabbits in another dimension then when Cain came back he kind of lost some of his memory i guess and go berserk but at the later time he came back. this second time with that giant ass white guy m'not sure of how they will solve it
my theory about gyeongjun (spoilers ahead and very long!)
i believe that gyeongjun has some hidden power within him. as a door, in chapter 3 cain mentioned that there is someone who is capable of withstanding the power of satan which cain prefer to is gyeongjun, for unexplained reasons sid didn't dare to kill gyeongjun because he sees something in him thru his eyes. to establish that gyeongjun has 'something', his eyes turn light blue in certain occasions, most of the time it can be seen whenever he and cain would do it but as the story progress this power would appear even without the presence of cain. idk but i feel we can know the answer from aron (doctor) because he's the one who i believe knows about gyeongjun's ability but as well he observes it (based on the raws) (it will start at chapter 31 i believe and would be discussed more in the raws) and on chapter 31, i translated a little bit on aron's dialogues about gyeongjun and he said that to cure cain's injury which is the bullet from satan which was struck by his chest was through gyeongjun's soul. another thing i lazy-translated in there was that to do that it has something to do with the power of love.
i believe, a normal door-demon relationship would consist of just violence and hate (e.g jinyeong and sid) which would destroy a person's soul but would benefit the demon, compare it to cain and gyeongjun they started kinda bad (not bad bad but good but like you get it righr???) and then as the story progress so does their relationship and turn intimate soon and became lovers which is something you would never find in a door-demon relationship. love will make your soul pure i believe and that's what happens to gyeongjun and since cain was struck by a weapon from heaven (that satan used) i believe gyeongjun would easily heal cain from it and rather absorb the weapon's power (based on what i think on the author's chap 78 twitter update)
this is not really complete and i think i've left out a few more but that's it i guess lmao