It sounds to be a filtered track. You can hear the original vocals at the end, at the part "So when...". Maybe you could do your own try of instrumental using RX9 or some other software. But if @NO17.tayeichi could share her version of instrumental, that would be awesome. By the way, good cover, and pretty great your version of the end, with a variation of vocals an the end, it sounds different but in a good way.