When do you think Yo Han fell in love with Ga On? I've always speculated that he fell in love during the show but maybe I'm wrong. Was it after the show ended? What moment triggered that? Just wanted to hear what you think :D
I personally think he fell in love during the drama, yes. But whether or not he realised he was in love during the drama is another question entirely. Though there, too, I'd say yes for my personal headcanon, most likely during the one-month time skip between the explosion and the hearing.
In that very classic: he and Elijah go off to Switzerland, he's suddenly without Ga On for an extended period of time, and that makes him go: "... well, fuck."
Because Yo Han is nothing if not aware of his own emotions (even if he likes to pretend he doesn't have them) and he would notice just how much he misses Ga On. And that the way he does it is unlike anything he's ever experienced before. And, eventually, put two and two together.
So the trigger for him realising is distance and his trigger for falling in love? Just... Ga On in general? x'D Like, I don't think there was one specific thing that made him fall in love. I think it happened in stages, one little piece at a time as Yo Han kept building his understanding of Kim Ga On. Because Yo Han likes to know how things work and study their components, but he probably didn't expect just how many of Ga On's he'd end up loving.
Like: oh, challenges me. Oh, he's actually really clever. Oh, he can cook. Oh, he's kind to Elijah. Oh, he's loyal. Oh, he's cute. Oh, he learns quickly. Oh, he's cheeky. Oh, he's playful. Oh, he's fierce. Oh, he's kind to me.
And so on and so forth.
Basically just a series of puzzle pieces that Yo Han collects and eventually he's just there. He's in love. Because to someone like Yo Han — who sees so many facets of a person and can read situations and people so well — I don't think one moment or one aspect would be enough? I think it would have to be ALL of Ga On.
That's not to say that he has to find every single trait Ga On has to be good or lovable, but I do think he needs to be fascinated. Intrigued. Curious. And that's why he's so fond of Ga On's darker side because it's exciting — it's an interesting, unexpected addition to this otherwise soft, doe-eyed young man. It stands in such stark contrast to Ga On's morals and righteousness that Yo Han can't help but want to see more of it.
And that's also why Yo Han loves how quickly Ga On learns, adapts, and picks up on Yo Han's methods. How quickly he adjusts and fires back, how quickly he can start turning Yo Han's own tricks against him. It's like Yo Han is trying to solve a Rubik's cube but if he waits too long, the colours will have swapped places when he wasn't looking.
And he absolutely loves it.
Long story short, I think Yo Han needs someone complicated with a lot of depth to keep him busy and engaged, and while Ga On might seem plain at first glance, he's definitely not. That boy not only has hidden qualities but is also clever and stubborn enough to give Yo Han a run for his money. And, clearly, that made Yo Han fall in love — and will make sure he stays in love.
So yeah. Something like that, I guess? I hope that answered your question xD