You are part of a special program in the Imperial Army of Japan. During WW2 you were a clone that were subject of tests and special mutations. Liquid were injected into you that helped you develop special powers, like better healing and vision. The most important of all, immortality. You will die eventually if you are exposed to limb/body damage beyond the rate of repair, but anyway you will stay young forever.
Among your hibernation grounds there were also 3 others. One whom you once called friend. For some reason your hibernation was interrupted when your friend tried to kill you. Being almost immortal your brawl was interrupted when 2 girls entered the domain and caused your "friend" to divert attention to the uninvited visitors. Soon you found yourself on the ground and were carried to safety by the 2 girls.
After a few word of exchange you were discharged from the hospital and went home with one of the girls that you saved. Meeting your clone you discovered that you have been dormant for almost 50 some years!