Sakanoue no Yuka is a fictional character based on a person who was likely real, but whose name is not known. In The Accidental Samurai she is the sister of Sakanoue no Mochiki, who was a real person. The names of Mochiki’s siblings, assuming he had any, are unknown. Yuka is a kind and smart person who values great art for art’s sake. If Mochiki had siblings this would likely have been true of them given his standing as a poet and the nature of Heian Era Aristocracy.