Artist: Nodoguro (Phi-tan)
Original title: 霧雨魔理沙が異形になるまで
Alternate title: 或ル魔女ノ×罪 (A Certain Witch x Sin)
Prequel to the series Wonderful Shrine Maiden of Paradise vs Creature that used to be an Ordinary Magician. Currently ongoing in twitter/pixiv with 3 chapters posted.