MuvLuv Unlimited

One day Shirogane Takeru wakes up late, wondering why Sumika or Meiya didn't wake him up that morning. Not seeing any signs of them he gets a bit worried, and goes out of his house only to see the town he lived all his life in ruins, and finds a giant robot destroyed outside of his house. After getting past the initial shock he convinces himself that it must be a dream and decides to enjoy it as much as he can. Soon he finds out the terrible truth behind the reason the world is in ruins, and meets people that look exactly like his friends from his original world.