Christmas eve's night. Coming back from a part-time job, a young man called Tomoki Ikeno saw a girl with silver hair collapsed in front of his house. She who called herself Reina, ended up living in Tomoki's house. Even though Reina was ignorant of the world, she was extremely skilled with computers, and it looked like she was holding some kind of a secret. But after a few days, a girl claiming to be Reina's older sister appeared, and was going to forcibly take her back. It turned out that Reina was the most important programmer of the military company Aegis and also a genius girl who single-handedly made the arms of national defense of this country. In order to escape the approaching pursuer of Aegis, Tomoki and Reina's aimless flight begins—