Yuki is one of twin sisters met by the main group at a rural inn. They were searching for their grandfather after mysterious Clockwork Dolls killed their mother; this tragedy prompted them to join Hiwou's journey.

Both sisters became vital members of the traveling group, enduring constant pursuit by the antagonistic Wind Gang alongside the protagonists. They had witnessed a plot to overthrow the government, making them targets and forcing their flight.

A key revelation occurs in Kyoto. Investigations into local intrigue uncover the sisters' true heritage: they are royalty, described as "princesses," with the added twist that one twin is actually a prince in disguise. This disclosure entangles them directly in the shogunate and imperial faction conflicts.

Their royal lineage proves critical later when their uncle, a castle lord, sentences them to death, compelling the group to mount a rescue mission. Their presence weaves themes of loyalty and strained family ties into the Meiji period's societal upheavals, shifting their role from vulnerable refugees to revealed nobility caught in high-stakes conflict.