Lisa Highwalker is a supporting character in the story of Unlimited Fafnir. She is one of the Ds, the girls who possess dark matter abilities and are enrolled at Midgar Academy. Lisa is the top student in the Brynhildr Class and serves as a member of the Dragon Subjugation Squad. She is sixteen years old and has very long blonde hair that reaches down to her knees, along with purple eyes. She comes from a wealthy family; her father, Mark Highwalker, and her mother, Linda Highwalker, run the High Walker Group, a major company in Western Europe.

At first meeting, Lisa comes across as harsh and cold, but this demeanor is a protective facade. Deep down, she is kindhearted and deeply cares for her classmates, viewing them as her family. Her initial antagonism toward the male protagonist, Yuu Mononobe, gradually softens as she sees his genuine nature. Lisa also harbors a strong animosity toward Mitsuki Mononobe because Mitsuki was forced to kill Haruka Shinomiya's younger sister, a traumatic event that makes Lisa distrustful of her.

Motivated by a desire to protect those she considers family, Lisa takes on a responsible role within the group, often acting as a dependable elder-sister figure. Though she once struggled with self-doubt about her own abilities, she never gave up and instead worked tirelessly to improve, eventually earning the trust and admiration of her peers.

As a D, Lisa can generate and manipulate dark matter. Her signature weapon formed from dark matter is a spear named Gungnir. She also possesses a small fragment of the authority of the dragon Vritra, which grants her a limited ability to interfere with her own fate. This power gives her a slight edge in combat against humans and also allows her to end her own life if she chooses. Over the course of the story, Lisa grows more confident in her role and learns to trust others, developing from a guarded individual into a loyal and protective member of the Dragon Subjugation Squad.