The island represented bits of the original family. Like how Jinhyeok talked to Romi initially and she told him about how much she wants a tree house and to become a famous author. And how she would love to live on an island, to be away from chaos but also finally free. He remembered that from the original Romi just to transpose that onto the fake Romi, and he automatically assumed each family member was the one from his adoptive family, when in reality they were all fake. I firmly believe that the ending is slightly ambiguous, and feel like that the 'monster' Jinhyeok won the fight on the boat before waking up, and his 'father' found it within himself to forgive whoever Jinhyeok was.
Been a long time since I commented the above. I think I had meant like, the physical island/idea that he could repent, was the physical island itself. Yes, it very clearly explains the people metaphors, but not the island as a landmass / safety / hope / not lost at sea
I mean? I think it’s interesting that the island crumbles when the dad leaves. It’s possible to me the island was something the dad brought in himself, not something jinhyeok had on his own. From Jinhyeok’s perspective, taehui was always there the entire time, and the fact that he went from the young look to the older look suggests to me a shift in how their minds were fused. I think the ending isn’t so ambiguous. I think he ended up calm, and even asks about his dad, I think this was the jinhyeok that repented, like how (the real) tarhui at least suggests he is repenting. Either of them may relapse, but at the end of where the story leaves off, I think he is mentally healed/in a moment of clarity.