Marion Benigni is a young girl who lives and grows up within the world of the Kaleido Stage. She is the only daughter of Jean, the chief set designer for the circus, and the late Cynthia, a former trampoline star who performed at Kaleido Stage. Marion was born and raised on the stage itself, which she considers almost like home. She is the youngest member of the main cast, even younger than the child performer Rosetta Passel.

Tragedy marked Marion's early life when her mother died in a freak accident during a performance. This loss caused Marion to become withdrawn and obstinate, closing herself off from others. However, her dynamic with the protagonist Sora Naegino becomes a turning point. Sora's warmth and persistence gradually help Marion open up again, and she develops a close friendship with Sora. Marion is also the primary caretaker of Jonathon the seal, a beloved animal performer at the stage.

Despite her young age, Marion shows a natural familiarity with the circus environment. She is deeply connected to the performers and the backstage crew. Her role in the story is largely that of a supportive friend and a link to the stage's family atmosphere. In one key episode, Sora and her friends work to convince Marion to return to performing on the trampoline, a skill inherited from her mother. This event marks a significant step in Marion's emotional recovery and her re-engagement with the performing arts.

Marion's notable abilities include her talent for trampoline acrobatics, which she initially shies away from due to the trauma of her mother's death. With encouragement, she demonstrates the potential to follow in her mother's footsteps. She also exhibits a natural ease with animals, particularly seals, and contributes to the backstage routine of the circus. Throughout the series and its related OVAs, Marion appears as a recurring supporting character, often accompanying Sora and the other performers in their adventures while continuing to grow more confident and expressive.