Set at the end of the 20th Century. Due to the Japanese Empire, an island country in the far east having been conquered by Caesar, a resurrected hero from Ancient Rome, it is now being controlled by the neighboring county Eastern Roman Empire! The power that made Caesar the most powerful conquered was called Legion. That is, a mysterious army made up of gathering all the great powers; a giant winged army. The Japanese empire's imperial princess, Fujinomiya Shiori, hides her ambition in becoming the supreme ruler and starts to act. Who she chooses as her trusted commander is, at first glance, a mediocre high school student Tachibana Masatsugu. However, he too is someone who was reincarnated from the past; a hero whose greatness rivals even Caesar's: Legatus Legionis!!