Claire Sesemann is a wealthy German girl who resides in a large mansion in the city of Frankfurt. Her father is a successful businessman often away on long trips, and her mother is deceased. Due to a chronic condition that prevents her from walking, Claire uses a wheelchair and lives a very sheltered and lonely existence under the strict and severe supervision of the housekeeper, Miss Rottenmeier. She has long blonde hair and is typically seen wearing an elegant blue dress with a large bow.

In the anime, Claire is portrayed as a sweet, gentle, and somewhat timid child. Her long-term illness and isolation have made her passive and quiet, as she is largely dominated by the rigid rules of the household. Despite this, she possesses a kind and patient heart. She is not selfish or demanding, but rather deeply lonely and yearning for friendship. Her life is given new meaning with the arrival of Heidi, a free-spirited girl from the Swiss Alps who is brought to be her companion. Claire is immediately charmed by Heidi’s cheerful personality and vivid stories of mountain life, finding in her a source of joy and excitement that contrasts with her own restricted world. She shows great kindness and patience, often defending Heidi against the strict criticisms of Miss Rottenmeier.

Initially, Claire’s primary motivation is to escape her profound loneliness. She forms a deep emotional attachment to Heidi, who represents everything bright and alive that is missing from her gilded yet sterile environment. As the story progresses, her motivation evolves into a quiet but determined desire for independence, culminating in her wish to walk again. Her role in the story is pivotal as the catalyst that brings Heidi to Frankfurt, setting the main conflict of Heidi’s homesickness in motion. Conversely, Claire’s own arc is completed when she travels to the Alps to visit Heidi, where the natural environment and her own willpower lead to her ultimate recovery.

The most important relationship in Claire’s life is with Heidi. The bond of friendship between them is the central emotional driver for her character. While Claire’s father, Herr Sesemann, loves her dearly, his constant absence leaves a void. Claire has a warm and affectionate rapport with her visiting grandmother, Frau Sesemann, who provides wisdom and gentle encouragement. Her relationship with Miss Rottenmeier is one of dependency and quiet obedience, as the housekeeper controls her daily life. The goatherd Peter acts as a minor antagonist to Claire out of jealousy over her friendship with Heidi, and it is his act of pushing her wheelchair down a mountain that forces her to try to stand.

Claire undergoes a profound transformation from a passive invalid to a more independent and healthy child. In Frankfurt, she is pale, weak, and entirely dependent on others. Her journey to the Alps marks the beginning of her change. Immersed in the fresh mountain air, eating simple food like goat’s milk, and enjoying the freedom of the outdoors, her health and spirit improve dramatically. The climactic moment occurs when her wheelchair is destroyed. With persistent encouragement from Heidi and support from Heidi’s grandfather, who carries her to the pasture each day, Claire begins to try to walk. She gradually succeeds in taking her first steps unaided, a triumphant personal victory witnessed by her overjoyed father and grandmother.

While Claire has no supernatural or extraordinary abilities, her primary notable ability is her strong willpower and determination. Once she decides she wants to walk, she perseveres through difficulty. Furthermore, her gentle and kind nature is a quiet strength that allows her to see past social conventions and form a deep, genuine friendship with Heidi, who comes from a completely different world.