忍び居茶臼 (しのびいちゃうす)

忍び居茶臼 (しのびいちゃうす)
男はあぐらをかいて後ろ手で体を支える。女は対面で男に抱きつき、腰を落として挿入する。別名、櫓 (やぐら) がけ。

Shinobii Chausu (Restrained Tea-grinding Mill)
The man sits cross-legged. The woman squats, facing him, onto his penis. Also known as "Yaguragake" (On the Tower).