Touhou EWI x Piano Collaboration - Satori Maiden ~ 3rd Eye (Satori Komeiji) Extended
Original arrangement and animation by winn: https://www.nicovideo.jp/watch/sm6435710
I didn't include this on the original Top 10 list for the simple reason that it's not one of the main EWI videos and thus didn't qualify. Shame, though, as this has some of the best and most clever visuals in the entire series with the Komeiji Sister's quick-change showcase between the playable and assist characters with Satori's danmaku changing up with each character.
And, let's be honest, seeing her get drunk while "playing" Suika's gourd is one of the funniest moments in the series too.
You may have also noticed that there's pretty much no point in the arrangement itself that allows for a natural song loop. Fortunately, just going back to the beginning with a brief pause at the very end actually ended up sounding a lot better than expected. I was expecting looping this would be a failure.