It's from a short flash animatic that was made for the Touhou clock project, a Touhou parody of Uniqlock. It was a web-based clock that would play 5-second Touhou flash animations on a timer to see how much time could be counted using Touhou animations. These animations were made by fans and submitted to the website. The artist that drew this one is credited as "セレン", but I couldn't find their socials. If you want to see some of the other animations, the project lead published recordings of some of them on their niconico. Kogasa here shows up around the 6 minute mark.
https://nico.ms/sm11268613
