(from ebookjapan):

Her kind and loving mother committed suicide⁉

Akiko, who cannot believe her mother's suicide, remembers that her mother had been acting strangely one week before her death.

It was because an alpine plant, black lily, was blooming in the garden. At her mother's funeral, a woman who had known her for more than 20 years appeared and left Yasukiko with the mysterious words:

"Be careful with the last Black Lily of the Hiryu family...."