Did you actually read all the previous chapters ? Because you're so off... Jin lost his memories due to Kimoto's blow to the head. Also, Jin didn't like Tehir manipulating Kimoto—not that he hated their relationship, he just didn't want Tehir to belittle or exploit Kimoto so he warned him many times about it (based on upcoming spoilers I discussed in another post).
Additionally, Jin liked Charin, but he never truly loved him (it was all one-sided from Charin's part actually, not Jin's) unlike Kimoto who was always head over heels for trash Tehir....
Kimoto never hit Jin on the head, he sliced part of his cheek off and then bit open his stomach. Neither of which would cause memory loss. Jin also states that he was aware he was thrown out/abandoned. And that he had a "mandate from the one before him" to learn to be human. Sounds like a message from his previous self to me.
It's also a fact that he was found with the blood knife thing sticking out of his skull, on it being the message about taking care of Jin. If Jin had lost his memories during his fight with Kimoto, why would he have stabbed himself in the head?
Manipulation and a sense of hierarchy was the foundation of Tehir's relationship with Kimoto. Saying Jin didn't like Tehir treating Kimoto bad, and saying that Jin didn't like their relationship is the same thing. Those two would not have interacted at all if Tehir didn't enjoy being "kind" to people he deemed inferior.
And regardless of rather you interpret Jin's feelings for Charin as genuine or not, their relationship still mimicked that of Tehir and Kimoto. Jin was absolutely obsessed with Charin to the point of dehumanizing himself, it was borderline religious.
Ok, i really want to give an answer to everything you mentioned that was inaccurate but there are too many things atp so i'll just focus on the essentials :
"And that he had a "mandate from the one before him" to learn to be human. Sounds like a message from his previous self to me." => The one who told him that he failed and ought to learn how to be human before evicting him from the airship was their teacher (the rhombus shaped figure, which we'll get to see more of in the next chapters btw).
"And regardless of rather you interpret Jin's feelings for Charin as genuine or not, their relationship still mimicked that of Tehir and Kimoto. Jin was absolutely obsessed with Charin to the point of dehumanizing himself, it was borderline religious." => I didn't interpret anything here. You are the one who suggested that "Jin viewed Charin the same way Kimoto did Tehir", so I responded that this wasn't really accurate, since Jin wasn't in love with Charin. That was not an interpretation on my part but what the author stated after being questioned by Korean fans about Jin's feelings following Charin's death.
Like, you're totally free to draw comparisons, but that doesn't mean they're correct. Jin followed Charin more in a puppy kinda way rather than viewing him in an overzealous or romantic way.
And btw, you said yourself that it was a "crackpot conspiracy theory with barely any evidence to support it", so there's no need to get defensive once someone presents you with the facts.
Anyway, I’m open to debate but since I’m no longer as enthusiastic about this story as I once was, I can’t promise that I’ll feel motivated enough to respond further, especially if confusion and misunderstandings continue to occur ~
Have a nice day tho ~
Eh? I'm not being defensive tho, I just think it's fun to talk about. That's why I posted the theory to begin with ( ̄∇ ̄")
If I'm wrong about certain things, that's fine.
I also wasn't aware the author talked in depth about character motivations in an interview. I keep up with the raws, but not with the author really since I don't have Twitter.

Alright guys, I got a crackpot conspiracy theory with barely any evidence to support it.
I think evil Jin "lost his memories" on purpose and made a new personality in order to be liked/accepted by others. And he modeled that personality off of Kimoto. (Maybe in an attempt to understand Kimoto better?)
When Jin was found he had a blade buried in his skull, seemingly made of his own blood. So an injury he gave himself to intentionally rewire his own brain, as Jin understood human anatomy freakishly well. He basically lobotimized himself on purpose. The new personality that emerged, imo, had striking similarities to Kimoto.
This could've been subconscious or intentional, but i think it was intentional. The new Jin was soft spoken, sweet, and intelligent. He also imprinted on Charin like a baby duck (the same way Kimoto did with Tehir) and hung onto his every word to the point of making himself dumb to make Charin happy.
Mild spoiler? But in a future chapter it's stated that Kimoto would have even killed himself if Tehir had wished it. These two viewed Tehir and Charin the same, and acted the same in regards to those feelings. Which is bizarre because evil Jin loathed the relationship Kimoto had with Tehir, as Jin was completely the opposite of Kimoto.
I kinda think evil Jin will make a return, but the two Jins will be like a split personality situation rather than Jin remembering and suddenly returning to who he was before.