Usagi-san

A small worn bunny plush with visible stuffing peeking out. She is tied to 3 heart-shaped balloons and floats in the air. According to the fanbook, one of her hobbies is singing with the flowers in the Wonderland SEKAI.

She is one of the many plushies that live and perform in the Wonderland SEKAI. Her appearance in that SEKAI is based on an old plushie once owned by Saki, which Tsukasa used to act out plays for his sister with when they were younger. Tsukasa had forgotten about the plushie over time, which hurt the plushie's feelings, but he remembered her later on in the Wonderlands x Showtime's Unit Story after spending time with her.