Dark nakige vn/borderline utsuge

[NoteSi]

Title

[Zalor]

It's more on the utsuge side, but Narcissu should fit. It's also one of the best VNs I read. 

[Clephas]

Karenai sekai to owaru hana

[Stormwolf]

Putting Eden up here in case you havent read it

[littleshogun]

I don't know on how dark you want when it come to nakige, but I guess Mugen Renkan here may be count although beware that it have several disturbing sex scenes (Not as disturbing as euphoria and Maggot Bait thankfully). For other recommendations and in case you didn't like disturbing sex scenes, I can suggest you Majokoi, Nanairo, Hoshimemo, Shinikiss, and Air. I hope that my recommendations here can be helpful to you