While Rachel was still a child, the X-Men’s base of operations was demolished by federal troops. The only survivor was her, whom the soldiers found by the side of Charles. They used drugs to neutralize her developing psionic powers before she was tortured&brainwashed in the lab of the sadistic Ahab. Following extensive behavior modification, Ray became a mutant “hound,” using her abilities to hunt down other mutants for the authorities. Her superiors branded her face with a grotesque pattern of tattoos to mark her&forced her to wear a leash (those fuckers). Summers occasionally killed mutants herself, but some of those were people she loved, which deeply scarred her soul, leaving her bitter toward humans who persecuted mutants.
Red and Blue Phoenix, by Rain Beredo.