Fuzuki is Mitsuki's grandmother. She initially hates music because she believes that music stole away everyone she loved. She is strongly against any music, and becomes angry when Mitsuki sings in her house.
In the anime, Fuzuki fell in love with a man who wanted to become a famous pianist, and the two were engaged. He became 'obsessed' with practicing piano, and when she suggested that he should relax a bit, he pushed her away and said she did not understand. Then he left Japan, and it broke Fuzuki's heart