Dang! This is good!
From the summary, while the idea is unique in IY fanfics, I thought it would be pretty predictable - survivors split to two groups, good and evil, and their true nature revealed as they battle it out to survive. But your first chapter had me hooked!
Brilliant idea by starting with a glimpse of the survivors on the island with a mysterious enemy instead of jumping right into the cruise to begin with. I thought this was a Sess-Kag fic (or hoping so!) so from that first scene I thought the lover on the beach was Sess and Naraku the enemy...but as I read on Naraku is not the evil being I thought (tho a bit of a sociopath as he himself says) but who's really lonely and it seemed you were knitting together a possible Nar-Kag pairing...so perhaps Naraku was Kag's lover on the beach? To be honest I'm a bit torn about that, I want Naraku to find happiness and can kinda see them together but really want Sess with Kag. (^^;
Loved how the enemy was the island or something on the island that possibly lured them / keeping them there, forcing them to work together. And man, Rin was creepy! Great job on the dark-horror side. Then you threw Mika and her dad in the picture...and Akito...
When you mentioned there was going to be a rape, I was thinking oh no which of the three girls will be the victim and which the offender...then you threw the twist. I never would've imagined...
The suspence, mystery was artfully done (you had my brain running crazy with 'What The Hecks' in c6!). c7 while providing interesting background, since there was only one more chapter left, I was skimming through that to get back to the action on the island...
I realise it's been two years since you last updated. I hope you're well and really hope you'll see this story through to the end. Thanks for sharing this unique story!