A 'Pillow Book' was a sort of journal in which one would jot down all sorts
of opinions, ideas and happenings as the mood took one. Sexual techniques do
not figure at all in Sei Shonagon's 'Pillow Book' though opinions of proper
and elegant way to conduct a love affair do. Sei and other Heian ladies were
not prostitutes or even courtesans, they entered into love affairs entirely
for their own entertainment or possibly with an eye to eventual marriage.

The 'courtesans' of Japan were the Tayu whose traditions and arts were
very different from those of the Geisha. There are no true Tayu today of
course but historical impersonators trained in their arts, (not including
sex).

No doubt many respectable Japanese wives resented the time their husbands
spent with Geisha and his Geisha mistress even more. They probably did consider
them no better than prostitutes.