Lin Kaifon is a woman with blonde hair and blue eyes who can summon a mystical armor to become the entity known as Brain Jacker, a transformation that enhances her natural capabilities.

Her past holds a defining trauma: an attack and subsequent mistreatment by the chimera Pegasus. This event shattered her trust in her allies, Mikoto and Ryuusuke, whom she believes failed to protect her. The perceived betrayal forged a solitary nature in her, leading her to believe she must face her struggles alone.

This isolation proved to be her downfall. Her judgment became clouded by a fixation on revenge, which impaired her innate ability to detect approaching chimeras from a great distance. Her defiant arrogance, particularly during her captivity, often provoked further punishment. Challenging Pegasus resulted in rougher treatment, and a defiant speech led to disciplinary action from orcs.

Her captivity involved repeated non-consensual encounters with Pegasus and orcs. An aphrodisiac was used to force a physical response she could not control, creating a deep internal conflict and shame. This treatment, along with the physical punishments, began to erode her pride and haughty demeanor.

This culminated in a moment of forced humility. After learning she was no longer needed for Pegasus's plans, she was compelled to apologize to him and admit her previous behavior was wrong. Though her apology was accepted, it did not save her from further discipline. She was then subjected to a final, severe measure of cold-blooded torture intended to break her spirit and soul, a punishment so extreme that only her screams remained.