The musical score seen in the opening scene is the beginning of the background music playing during the scene in Oktavia's barrier.
The chairs seen in Madoka's bedroom may be an homage to Bokurano, a manga and anime series that deconstructed a children's mecha anime called Zettai Muteki Raijin-Oh. In Bokurano, children are called by a strange man and an evil-looking mascot character to pilot a giant robot and defend their world from invaders from an alternate time-line. If they lose, the loser's universe is destroyed. They are also told by the mascot only after the first battle that the robot's fuel source is the life of the person who pilots - in other words, each of them will only be able to pilot once. Accordingly, the first pilot slumps down and dies right after the end of his battle. The chairs in Bokurano are reflections of the personalities of the selected pilots, drawn from their memories and manifested in the robot's cockpit. After a pilot dies, their vacant seat remains.