Since Takashi Natsume moved a lot before he came to live with the Fujiwara family, he was being passed along from relatives to relatives.
The first episode in Natsume Yuujinchou Zoku. These were the relatives that gave Reiko Natsume belongings to Takashi Natsume. When seeing the Book of Friend, which according to them just full of scribbles, the female relative said that they always knew that Reiko was pretty wild back then, but they didn't sure that she was that out. Takashi, hearing that, just staying quiet and relishing his inheritance of his late grandmother.