Yuika and Sou were in the same class in the first year of junior high, but not in the second. They became classmates again for their third year when they were in Class 3-3 together. She tells Sou that his personality resembles her brother's and that she has noticed how he has been withdrawn and aloof for the last few years. Sou is initially unaware of Yuika's feelings towards him, and often treats her coldly despite her attempts to get to know him better.
Yuika later admits that she chose to be a non-existent student in order to be with Sou, and that she felt more reassured that they were in the same situation together. She becomes jealous of how much time Sou spends with Izumi Akazawa. Yuka eventually becomes distant from Sou after renouncing her status as a non-existent due to the overwhelming treatment and isolation she received from her classmates.