Chapter 8: Danchi
After their exams, Shijima and Majime have received disappointing scores, so the latter proposes to start another study meet at the former's residence. Initially hesitant, Shijima eventually agrees and guides Majime to the apartment complex where she lives with her sister. Along the way, they stumble upon a peculiar black cube by the roadside, which Majime mistakenly assumes to be Shijima's house. Since the front door is currently inaccessible, the two girls decide to enter Shijima's apartment through the veranda, which had incurred damage due to a recent explosion apparently involving a mackerel. Majime discovers the hard way that the apartment's security measures against intruders consist of scattered spare components strewn across the floor, all of which are important for Big Sis' experiments.
While the girls review their math scores at the apartment, Big Sis informs them that they can attend additional lessons if they fail their finals, much to Majime's despair. Neither of the students wanted to, so Big Sis proposes that she will assist them in preparing for their finals on the condition that they help her with "more dangerous work" related to her new invention. Majime then discovers Shijima's living space, which turns out to be a cramped closet illuminated by a single light bulb. She deduces that this must be where Shijima "grew" her shimeji mushrooms in the first place. Majime desires to enter the closet, only to be rejected by Shijima. Afterwards, Shijima and Majime dedicated a few days to assist Big Sis in assembling her machine, going to the extent of requesting time off from the Hole-Digging Club. As time went by, the device gradually neared its completion...
