Midori Makibao is a small white racehorse who, compared to other thoroughbreds, resembles a donkey with wide nostrils. Despite his unconventional appearance, he relies on determination and speed to win every major race. At the start of his career, Makibao struggled to debut as a racehorse because of his looks and various disadvantages. However, he has clear motivations to overcome these challenges: a lifelong rival, the champion Superhorse Cascade, whom he must defeat, and a desire to recover his mother, a mare taken away to settle the farm’s debts. Makibao faces many hardships, but he thrives in the series of races.