Thanks for the comments!
It is really hard to remove vocal tracks from songs, especially when the song has a pretty busy arrangement, because they often mix in sound effects or instruments with the vocal track and it requires a lot of editing to get them clean. I had to do multiple hours of work on this vocal track just to get it as clean as it is in the track you hear
Mai's solo is the part that has the most remnants of the original track left, because they had the keyboards that play during her solo panning back and forth through the left and right channels so it was constantly in the track no matter how I tried to edit it, but I did as much as I could.
You can also check out my other idol mixes (AKB, H!P, etc.) through the link in my signature here, if you haven't already, but this is the first one I've done with Idoling!!!