She is diagnosed with an unknown illness and has been bedridden for two years. Within this period, Otonashi (Yuzuru) acts as her guardian, usually visiting her to give her manga to read and to keep her company. Compared to her brother, Hatsune enjoys studying and hanging out with her friends. However, her sickness kept her from going outside. She is also gifted by her brother's love, who despite having a meager income out of part-time jobs still has enough money to bring her comic books which she enjoys reading. Her gestures of gratitude, in turn, reassures him.
SpoilerUpon her last request to go outside to see the decorations outside the hospital where she stayed, she passed away, clinging on to her brother's back on her final moments.