Yukiko Comes up with the idea of her "older sister" getting taken away by Ayumi
Takahashi Macoto (mangaka) Deborah Shamoon (author of book the picture is in)
Sakura Namiki (Title of manga) Passionate Friendship: The Aesthetics of Girls Culture in Japan (book with the picture in it) chapter 4 The Formation of Postwar Shojo Manga p. 93