Based on a short section of the novel Cuore by the Italian Edmondo de Amicis, Marco is a young boy living in Genoa, Italy, together with his father Pietro. But the family is not complete, for Marco's mother left for Argentina around a year earlier in order to find work. Letters from her arrive regularly until one day they suddenly stop. Worry for his mother and what might have happened to her overcomes the young boy. Marco thus decides to embark upon a journey to Argentina in the hope of being reunited with his mother. At first, Pietro is opposed to Marco's plan, but moved by his son's enthusiasm, he eventually allows the boy to go. So begins Marco's long journey of the heart. Marco encounters many people throughout his travels, and finds maturity and self-acceptance as a result of his experiences.

(Source: Nippon Animation)