Assuming this is your theory and not a spoiler, I’m going to base some thoughts on that. Sorry about the misspelling of names. So you think the guy with the long white hair is the childhood friend, but he didn’t die? Maybe the death was faked and the sister was in on it with the twin to keep Fukatsu away from kyuske since the other girl said the sister didn’t want him around that Kid? I guess the long white hair guy is wearing a wig if he’s Kyuske and supposedly bald. But if he was actually the one who was rescued from the water (cuz black wig guy said it wasn’t himself) wouldn’t he have been bald in their memories of the rescue? But the rescued guy had white hair with a black wig. Also makes me wonder if one twin was the weird one that did all those crazy things. Lol, I know I threw a lot out there, but my mind is all over the place on this.
The other guy is kosuke. This white hair (who had black wig) is his twin that's y he has grudge on futaku.