To Rekindle the Sun

As the thousandth year approaches Princess Celestia falls into a mire of guilt and depression. Twilight Sparkle decides to fix things.

Nearly a thousand years have passed since Nightmare Moon was banished. As the old memories well up Princess Celestia is crippled with guilt and depression over the loss of her sister. Her faithful student Twilight Sparkle takes it upon herself to make her teacher happy again by giving her what she wants more than anything else in the world.