Utsukushiki Zankoku na Sekai by Yoko Hikasa - Attack on Titan ED1. The melody is a startling contrast from the anime itself. Unlike the action packed and destructive anime, the song is gentle and pure, sad and foreboding, but with a measure of strength. Like someone (namely Mikasa, featured in the video) desperately fighting to hold on to something that will inevitably escape their grasp.