My mother's side is Ainu Japanese, actually. My father's side is not, father's side is of Watanabe Clan in Japan. Ever heard of Watanabe? It is an ancient clan, as old as the Abe clan, it originates since the Yamato period.
My father's family have a large shrine in Sapporo, and from it I can trace back my ancestor from 9th century CE.
No they are not "pure" Japanese but I don't think it's an issue in our family. My dad married my mom who is Ainu ethnic. In fact I'm Half Ainu, half Yamato Japanese.
Btw, my cousins were very close to my grandmother. She always cry so bad whenever they leave and go back to Guangzhou . She always try to encourage my uncle to leave them in Japan. But my aunt doesn't want to leave her family in Guangzhou.
My uncle stays in China because he loves my auntie....