Promises Are Forever

Severus Snape
Everyone knows about him, and about his shadow of a twin sister, Silver (Severus usually takes to calling her Silly to mock her attitude)
Silver and Severus were impossible close. Wherever one went, the other was there.
But what happens when Silver, the most powerful witch of her time, has to defeat Lord Voldemort herself but in order to do so a sacrifice Has to be made..

..A sacrifice of love

~Severus POV~
I couldn't help smiling a little as James ran up to me, crying and repeating "We did it! We won the fucking war!". I pushed him off me lightly and kissed him before realizing something, "Where's Silly?" I asked pulling away from James.
I looked around and realized she wasn't there and I started to panic a little. The worst possibilities were going through my head when I noticed a blinding flash of light outside, and only one person could make a light that bright.
"Silver! Silver, no!" I screamed running towards her. I knew I wasn't going to make it in time. Her skin was on fire and Voldemort was crumpled on the floor. I kept running anyways. "Please, no!" I kept screaming thinking, 'I can't lose her. Anyone but her'. It was only when I was so close to her, I could feel the heat radiating of her, I felt someone drag me back from behind. It was James. He had been running after me but I hadn't noticed because I was too focused on Silver. Speaking of Silver, she was saying something, "Severus, I love you but this was the only way I could protect you. Just like I promised."
"No please! I don't care about some stupid promise, just don't do this!" She turned back to look at me and I noticed that, although she was burning, she had tears streaking down her face. "You may not care about the promise but, Sevy, I've never broken a promise I made to you and I'm not starting now." And with those last words, my sister exploded into a pile of dust falling from the sky with only my screams to fill the silence.