Born and raised in Iselia, a village in the declining world of Sylvarant, Colette Brunel was identified at birth as the seventh Chosen of Regeneration due to the Cruxis Crystal in her hand, signifying her destiny to regenerate the world by ascending the Tower of Salvation. Raised by her adoptive father and grandmother, she knew from a young age her role required self-sacrifice, cultivating profound selflessness. This led her to conceal the fatal outcome of her journey from her closest friends, Lloyd Irving and Genis Sage, whom she met at the Iselia schoolhouse.

An oracle from Cruxis initiated her Journey of Regeneration on her sixteenth birthday, requiring her to release five seals across Sylvarant. Initially accompanied by mercenary Kratos Aurion and teacher Raine Sage, she was later joined by Lloyd and Genis after their banishment. As the journey progressed, Colette gradually transformed into an angel, gaining enhanced sight, hearing, and wings while losing human traits like the ability to taste, sleep, speak, and feel. She attempted to hide these changes from Lloyd, though he eventually discovered the truth.

Reaching the Tower of Salvation, Colette sacrificed her heart and memories to become a vessel for the goddess Martel's resurrection. Remiel, her assumed father and guide, revealed his deception. Before Martel's consciousness fully merged with her body, the Renegades rescued Colette, taking her to the parallel world of Tethe'alla. There, Lloyd restored her consciousness by carving a Key Crest into her necklace; she retained her angelic powers but contracted Chronic Angelus Crystallus Inofficium, a rare angelic disease causing painful crystallization. She concealed this condition from embarrassment and to avoid worrying her companions.

During the Tethe'alla arc, rogue Desian leader Rodyle abducted Colette, intending to use her Cruxis Crystal for a mana cannon. Discovering her crystal was inert, he abandoned her; she was rescued by Lloyd and the party. Rodyle condemning her as a "sinful and useless Chosen" deepened her guilt over failing to regenerate the world. Her disease worsened, manifesting as visible arm crystallization after she intercepted an attack meant for another.

Later captured in the Tower of Salvation, Colette was forcibly merged with Martel's consciousness. Martel used Colette's body to condemn Mithos, while Colette sensed Martel's subconscious plea to stop him. After Zelos Wilder applied a Key Crest to her Cruxis Crystal, Martel's consciousness departed; Colette revealed she understood Martel's sorrow and desire to end Mithos's tyranny.

In the final confrontations, Colette's actions varied. If she shared a pivotal conversation with Lloyd in Flanoir, she intervened during the battle against Origin, allowing Mithos to possess her instead of Lloyd. Her strong soul later overpowered Mithos in Derris-Kharlan. Otherwise, she confronted a mirror image of Remiel who chastised her for abandoning her duty. During the climax, she attempted to persuade Mithos to surrender by invoking Martel, though unsuccessfully.

Colette's characterization included notable clumsiness, often causing accidents that yielded fortuitous outcomes, sometimes interpreted as divine intervention. She demonstrated unwavering self-sacrifice, prioritizing others' safety even against assassins, and frequently deferred to Lloyd during critical decisions due to lingering self-doubt. Her deepest longing was for an ordinary life, while others bore their destinies with resignation.