Hihon: Sode to sode (1974)

Writer and ladies-man Yonosuke, who gives inept English lessons (using Shakespeare's Romeo and Juliet), is mistakenly ushered into the back entrance of a woman's house one rainy night. When he finds out that her husband is away at war in Russia he tries to take advantage of the situation. Her honor is saved when he discovers she is wearing a chastity belt. But she is lonely and she has the key...