Responses
I think it was when he was kidnapped. And he doesnt even know why he hates him, the feelings probably belong to his past life (remember he met his past self too).
He first met him when he was a child, he told him the secret for the 1st mugo to take over and prevent him from being eaten, then the second one was he got kidnapped, he was angry because he got kidnapped by lee, he does not recognize mugo and lee the same because mugo is the present lee is the past, even the old jae told him to let go.
I am a bit lost please remind me when did the MC meet Lee Muhan? Which ch? And why the fuck does he hate him soo much?