Long ago, there existed two different groups of people. One had red blood and the other had blue blood. They co-existed peacefully, but eventually they started to hate each other and a war broke out.

The massive red blood army initially overwhelmed the blue blood but with the help of new technology developed by Kodo, the prince of the blue blood, the blue bloods were victorious. The new technology, called the Haguruma, is a powerful robot type machinery capable of devastating destruction.

As the red blood people were enslaved, Kodo saw what monstrosity his Haguruma was being used for. Helpless red blood people were being hunted down and murdered. Overwhelmed by guilt, Kodo rescued the refugee red bloods and refused to build any more machines. His father, the king, ordered him to be executed, but he barely escaped and now without a home, he must survive on his own.

(Source: MangaHelpers)