For a little context, this is kakifly's currently only modern day artwork that isn't of K-ON!
It comes from a doujinshi called "セーラーミズギノホン Vol.4" by CYTOKINE. It's been out of stock ever since it was sold and I only managed to now find a copy of it.
CYTOKINE is the brother of ZYTOKINE who kakifly has also worked with in the past by doing the illustration of the album artwork of Touhou Project's Double Key doujin album back at CM83