Midori Makibao is a small white racehorse. Compared to other thoroughbred horses, he looks more like a donkey with wide nostrils; however, with his guts and speed as his weapon, Makibao wins in every big race.

In the beginning of his career, Makibao had a trouble making his debut as a racehorse, because of his appearance and various disadvantages he had. But Makibao had reasons to overcome his difficulties; there was a lifelong rival horse called Superhorse Cascade, that Makibao needed to defeat. Plus, he was determined to win back his mother, a horse that had been taken away for pay back the debt on the farm.

There are many hardships that Makibao has to overcome, but he thrives in the series of races to become a great racehorse.