This is a oneshot doujin by Shima Tokio (Oshibana, Dachi no Imouto, Gemini wa Otoshigoro author) released for a doujin event earlier this month.
If you enjoyed this, please help me ease some of my guilt for pirating something the author is directly profiting from as it's self published and support the author by buying the original at the following link (it's only 200 yen! They take paypal!):
https://shima173.booth.pm/items/4734945