Hisca Aiheap, a human Imperial Knight of the Niren Brigade from Zaphias, serves alongside Yuri Lowell, Flynn Scifo, and her younger identical twin sister, Chastel Aiheap. As the older twin, Hisca holds a higher rank than Yuri and Flynn. Identical to Chastel with red hair and yellow eyes, Hisca is physically distinguished by her flatter chest. Their personalities contrast sharply; Hisca displays a more stubborn and less gentle demeanor than her sister, frequently reprimanding Yuri for his impulsiveness during missions.

Hisca specializes in military operations employing a sword and magical blastia devices. Early on, she demonstrates a Force Field blastia during a monster extermination and later shows Yuri her Bodhi blastia, equipment not issued to rookies like him. During a critical incident in Shizontania, Hisca helps defend the town against an aer-energy monster. This confrontation triggers Lambert, a wardog, into uncontrollable rage. To protect Hisca, Yuri kills Lambert. She later participates in investigating an aer-gushing fortress, witnessing Captain Niren Fedrok sacrifice himself to ensure the team's escape during the structure's collapse.

While absent from the original Xbox 360 release, Hisca appears in the PlayStation 3 version and Definitive Edition via a specific sidequest. Her character development across these appearances remains consistent, focusing on her knightly duties, relationships within the brigade, and her contrasting dynamic with her twin sister.