Looking For Fic: Harry Joins Voldemort
This is an old fic that I remember stumbling upon online ages ago. It was hosted on its author’s own website and it was VERY dark. Basically Harry agreed to be trained to defeat Voldemort but it turns out he’s signing up to be experimented on and abused by Snape and others to turn him into the perfect soldier, including activating latent Incubus heritage in his heritage that leads to Snape and others sexually abusing him to feed him.
He regains control and flees to Voldemort and begs for protection and ultimately joins his side as Lord Xanatos (iirc), and he and Voldemort proceed to kidnap his former friends who it turns out all pretty much turned on him. He leaves Remus alive but locked up as a dog to redeem himself, and he lets Neville and Luna go live new, free lives far away. But everyone else he and Voldemort torture to death.
The fic ends with them subduing and defeating Dumbledore. I also recall a recurring thing where either Draco or Lucius keep walking in on them having sex.