Jin and his clubmates Daitetsu Hibiki and Meguru Akiba receive the task of cleaning an old storehouse from their seniors at the art club. Upon arriving there, Jin finds a spider-like impurity wandering there, but he ends up hiding the fact from Nagi. However, she becomes suspicious about his behavior and borrowed one of Tsugumi's spare uniforms to infiltrate the school. Nagi tagged along Jin and his classmates to figure out the mysterious being knocking from the cellar at the storehouse, just to find out that it was a teacher from the school whose studio lies under the floor. Nagi continues to search for the spider-like impurity, only to find a mysterious girl, who addresses Nagi as her older sister, easily destroying it.