Somnus is a Gallade Pokemon but is surrounded by some sort of strange, evil energy or "aura."
Somnus is the main antagonist of Dear Brother. He was friends with Melanthios and Photios' brother when they were young. Something happened to Somnus when he was older (about 13). His parents were murdered one day and no one suspected that their only son, one of the nicest Pokemon in that area, to be the murderer. Luke began to suspect that there was something wrong with his friend and decided stay away from him because he knew that Somnus was the murderer. He would have fits of anger and madness randomly and soon became driven completely insane. This goes on for about another two years.
Photios and Melanthios come into this story when they and Alya venture out into the forest. They wander very far from the two brothers' home and saw Somnus repeatedly stabbing a Gardevoir in the back with a blade that was long enough to exit out of her chest and stomach area when stabbed into her. Somnus saw them an the three ran. Since then, Somnus became power-hungry and blood-thirsty. He planned on destroying the town he grew up in one person at a time until the evil power that corrupted him grew strong enough for him to take over the world.