Rachel, also known by the alias Michelle Light, is an Irregular who enters the Tower with the goal of reaching its summit and seeing the stars. Before her entry, she lived outside the Tower and was the only person to visit Baam in the dark cave where he was confined, becoming his sole friend and teacher. She taught him language, basic knowledge about the world, social manners, and stories, and she was the one who told him the tale of a man who built a tower to reach a star he loved. Her longing to see the stars is tied to her fear of darkness and night, and she hopes that climbing the Tower and standing at a place near the sky will allow her to obtain a light of her own.

Rachel's personality is defined by contradiction and inner conflict. She appears as an ordinary young woman of unremarkable appearance who is keenly aware of her own lack of special talents, and she resents those who are beautiful, gifted, or favored by circumstance. She is manipulative and deeply self-righteous, able to justify harming others in pursuit of her ambitions, yet she is also self-aware enough to admit that she is sly and that her actions have driven people away. Her desperation to succeed coexists with guilt, self-loathing, and a fragile sense of self-worth. She is obsessed with reaching the top of the Tower and will use anyone or anything to move forward, but her deeper desire is to become someone special, to shine as a star herself rather than remain an ordinary girl in the shadow of others.

Her central motivation is the dream of seeing the stars from the top of the Tower, an ambition that is outwardly modest but carries enormous personal weight. She fears darkness and seeks salvation in the light of the sky, and she believes that climbing the Tower is the only way to escape her ordinary, limited existence. That desire is so strong that she is willing to betray, deceive, and abandon the people closest to her, including Baam, to keep climbing.

In the story, Rachel serves as a driving and antagonistic force, especially in the early part of the series. When she first enters the Tower, the guardian Headon tells her she was not chosen to be a Regular, but she refuses to accept this and makes a deal that allows her to climb under certain conditions. As part of that arrangement, she is drawn into a plan that requires her to betray Baam. She keeps a distant and guarded attitude toward him during the tests, and in the final test of the first season she pushes him out of a shinsu bubble and sends him falling, leaving others to believe he died while protecting her. Afterward, she continues her climb under the name Michelle Light, posing as a Light Bearer and at times pretending to be crippled so that others will carry her forward. During the Workshop Battle events of the second season, Rachel does not directly participate in the main conflict, but her prior actions and ongoing schemes continue to influence the situation. She reappears working alongside dark forces and uses her knowledge and cunning to secure a place on the path upward.

Rachel's most significant relationship is with Baam. She was the center of his world in the cave, and he viewed her as more important than anything else, while she saw him as her light in the darkness. Her jealousy of his natural abilities and his role as a chosen one, combined with her own insecurities, leads her to see him as a rival standing in the way of her dream, and her betrayal of him is the defining act of her character. She also interacts with Khun Aguero Agnis, to whom she confesses part of her past and asks that he keep her survival a secret from Baam; in their few direct encounters, Khun easily outclasses her. She feels envy toward women like Androssi Zahard, who possess beauty and natural talent, and she forms alliances with stronger individuals when it serves her purposes, though most of those bonds are temporary and transactional. Figures such as Headon and Hwa Ryun also use her as a tool in their own designs, exploiting her desperation.

Rachel undergoes significant development over the course of the story, shifting from a seemingly kind and protective companion into a calculating and ruthless climber. Her betrayal of Baam is not portrayed as a simple act of evil; she hesitates, feels guilt, and struggles to accept what she has done, yet she refuses to abandon her dream. After pushing Baam away, she experiences a breakdown, and her later actions show a woman who has convinced herself that her goals justify her cruelty while remaining haunted by insecurity and self-hatred. She repeatedly avoids direct combat and relies on deception, strategy, and the protection of others, a pattern that reflects both her physical weakness and her willingness to make others pay the price for her advancement.

In terms of abilities, Rachel possesses no extraordinary combat power or notable shinsu control, and she is easily defeated by stronger Regulars in direct confrontation. Her strengths lie in her intelligence, her knowledge of the Tower, her ability to read and manipulate people, and her talent for forming strategic alliances. As a Light Bearer using the alias Michelle Light, she operates in a support role with a Lighthouse, directing information and providing guidance to her team rather than fighting directly. Her apparent disabilities in part of the story are revealed to be a pretense, showing that her greatest weapon is her ability to deceive others into underestimating her while she pursues her goal of reaching the stars.