This type of erotic book with fold-out pages, giving the story an element of animation – is called shikake-hon. This example is by the author Enba II and Kunisada and each volume comprises a single-page portrait of a woman, followed by two stories illustrated on double-pages, a single-page picture of a woman’s genitals, followed by a four-page story.
See Timothy Clark ed., Shunga: Sex and Pleasure in Japanese Art, (London, 2013), cat. 116, p. 388.