G.O.D: Mezameyo to Yobu Koe ga Kikoe

The year is 1999. A boy named Gen lives together with his mother in a small Japanese city. One day he goes to the nearby mountains and discovers an underground cave. In this cave, he encounters a strange bat-like creature guarding what appears to be a huge diamond. When Gen approaches the diamond, the floor crumbles, and all he can see is a group of aliens descending on the Earth... Gen is awakened by a man in a military uniform. He quickly gets up, and notices a calender. The year is 2009! Ten ...