From what I remember there were three sides of the story. The human race, a special organization that "protects", and a group of kids with abilities that were deemed dangerous to humans and hunted down. Sounds almost like a comic lol, but way better. The protector of the special kids could transform into a monster with a split face (two different colors) and couldn't die. He was actually centuries old, and carried the hatred of what had happened to his village. One of the kids was a girl with an incredible and magical voice. When she sang the organization could track her. It was complicated and had a great storyline! Has anyone else watched this, and do you remember the name of the show?
Sounds a lot like Towa No Quon, a 6-part OVA series, has a transforming ancient protagonist and a girl with a magic voice. https://en.wikipedia.org/wiki/Towa_no_Quon
Main character transforms into a monster to save his friends, who have special powers, from a secret organization that is hunting them. His village was destroyed and he's got a healing factor + immortality.