Chihiro was the younger brother of Takashi Yanase, creator of Anpanman, born roughly two years after Takashi. The brothers grew up together in Kōchi Prefecture, Japan, raised by relatives after their father's absence and their mother's remarriage. After their father died during an assignment in Shanghai, they lived with a paternal uncle who practiced medicine.

Chihiro served as a junior officer in the Imperial Japanese Navy during World War II. He was killed in action off the coast of the Philippines during the Pacific Campaign. News of his death reached Takashi in 1946, soon after Takashi returned from his own military service and imprisonment in China. Chihiro's loss profoundly impacted Takashi, compounding his wartime trauma and disillusionment with heroism and sacrifice.

This death became a catalyst for Takashi's philosophical struggles concerning justice, heroism, and the meaning of life. These themes permeated his creation of Anpanman, evident in the hero's selflessness and the series' messages about hope amid adversity. The poignant questions in the "Anpanman March" theme song—"Why was I born?" and "What should I do with my life?"—are interpreted as reflections on Chihiro's abbreviated life and the futility of war.