"Alps no Rōjin Heidi no Ojii-san" is an anime adaptation of Johanna Spyri's classic novel "Heidi," set in the Swiss Alps. The story centers on Heidi, a spirited and kind-hearted young girl who is sent to live with her reclusive grandfather, known as the Alm-Uncle, in a remote mountain village. Initially, the Alm-Uncle is gruff and withdrawn, having isolated himself from the community due to past hardships. However, Heidi's cheerful and compassionate nature gradually softens his demeanor, and the two form a close bond.

Heidi thrives in the idyllic mountain environment, befriending Peter, a local goatherd, and spending her days exploring the natural beauty of the Alps. Her life takes a dramatic turn when she is taken to Frankfurt by her aunt Dete to serve as a companion for Clara Sesemann, a wealthy but frail girl confined to a wheelchair. In the city, Heidi struggles to adapt to the rigid and restrictive lifestyle, longing for the freedom of the mountains. Her homesickness and unhappiness affect her health, and Clara's family eventually realizes the toll the separation has taken on her.

Heidi returns to the Alps, where her grandfather welcomes her back with open arms. Her presence continues to have a transformative effect on those around her, including Clara, who visits the mountains and experiences a profound improvement in her physical and emotional well-being. The story emphasizes themes of resilience, the healing power of nature, and the importance of human connection. Through Heidi's unwavering optimism and kindness, the narrative highlights the impact of compassion and the ability to find joy in simplicity.