Silver Petals

(from ebookjapan):

Hideko Mizuno, the mistress of Shojo manga, depicts the adventures of a young girl, Lily, who is tossed about by a strange fate, and her brother, Peter, who becomes a silver knight and fights to save her in this long-form theatrical romance.

Lily, and Peter live happily with their grandfather, who also taught Lily to play the violin. Their grandfather goes with Peter, who offers to be an emissary to the Mauquerre, who demands a hundred gold coins from the Red Dawn Brigade, and to deliver the gold coins to the "lonely pass," a designated place.... ...?