Torii Ui

One of Yuri's former neighbors who is an otaku and loves cosplay. She moved out because of her parents' situation but came back a few years later; however, her parents couldn't come back with her because of their long business trip, so she crashes into Shinobu's house for the time being and pretends to be his little sister. Ui is an honor student who is good at sports and all subjects, but also very knowledgeable of sex (thanks to a thin notebook solely made for otakus) and interested in playing eroges, which she hasn't done before. She also likes being spoiled.