She was Shuichiro's mother, although not biologically. Hotaru disappeared when Shuichiro was 15 years old. She has the appearance of a beautiful young girl and is unable to walk or see.
(Spoiler: Hotaru is actually the spirit of the Wistaria tree in Shuichiro's backyard, which is why see can not walk or see. Shuichiro was in love with her, but Hotaru loved his father. She told him that her "string" did not tie her to him and that his string tied him to someone else.
Vova
