I think I know a worse Visual Novel. Dustmania. It's about as bloody as Saya No Uta, but worse.
Basically, it's about a perverted Mad Scientist kidnapping an immortal girl to do horrible things to her, to use her as a live infinite test subject/torture victim who she doesn't have to worry about killing. And she does some things that I wish I could forget (like gouging her eyes out with a knife, and literally raping her in the brains).
You said you wanted to find a worse one. Well check it out at your own risk.