Chigo-zoshi(1321); the picture scroll which is owned by Kyoto Daigo-ji Temple.
Sodomy stories with a Buddhist priest and the young boy. And this is the one of the cuts of stories.The anal sex was the norm in monk-chigo(a young boy who serves to his master) relations in those days.
This picture is from the story; Buddhist priest found his penis was not able to insert. So he expanded the hole of buttocks of the young boy who serves him.