Jennifer Christina "JC" Armack is the sister of John "JC" Armack, a character starring in the related video game series. Her brother died after assimilation by a mutant entity during a HardCORPS operation in Freeport City's sewers. This occurred when he investigated a mysterious red glow, encountered a biological mass absorbing him, and ordered his partner to kill him before the assimilation completed.

Serving as a Universal Army intelligence specialist, Jennifer blames Colonel John Blade for her brother's death. At her brother's funeral, she confronts Blade, demanding custody of Elise—a young girl rescued from the same entity—and accuses him of connections to organized crime.

During the assault on SinTEK's headquarters, Jennifer participates in the confrontation against the corporation's forces. She witnesses fellow officer Tim Perko sacrifice himself by stabbing to prevent assimilation after an attack by the mutated Vincent Mancini. This experience contributes to her shift from personal vengeance toward cooperating with Blade to combat the mutant threat.

Demonstrating technical aptitude, Jennifer attempts to override security lockdown systems during missions. Her arc culminates in aiding Blade to infiltrate the SinTEK tower, rescue Elise, and confront the corporation's leader.