The songs used as each opening in the anime are numbered, however each volume only goes up to 9 openings. The number keys work with their respective openings (However OP 19 and 20 use different buttons, which are [0] and [Space] respectively) and will stop all other sounds when pressed, with [Up Arrow] being the key that stops all songs and doesn't play any others after.
Im giving huge credit to StardustPhoenix1234 for making. Not saying he did anything wrong, just fixed his Blood Circulator to a long and extended version.
