You’re just going to have to take my word for this and I can’t explain why or how but: nunsploitation is a quite significant genre of Japanese sex film even though (or perhaps because?) there are very few nuns or Catholics in Japan.
Runa’s Confession stars former pop singer Takamura Runa as a young nun, back from the convent and bent on revenge against her sister and her former lover. She reportedly has come to them with a get-rich-quick scheme to make money and, of course, spread the Good News of our Lord Jesus Christ by buying property in Africa. Her sister is already wrapped up in some underground business selling ink prints of her vulva to middle-aged men (this is an actual plot point, I am not joking, would I make that up? This is not even the only movie where someone makes ink prints of female genitalia as a major part of the plot. Suspect it has something to do with the ban on showing genitalia in media.) The former lover is a world class loser, too, so it’s easy to cheer Runa on as she uses them and tosses them aside.
Typical to director Konuma Masaru’s work, there is a great deal of violence: Runa is brutally raped by a priest and part of the vengeance involves her sister being raped by the men who buy her pussy prints. Rape and extreme violence were a common feature of sex films at this time (and in most other times.) In the midst of these violent relations is an unexpectedly sweet but understandably fucked-up lesbian liaison: Runa connects with a fellow nun, Yuki, who comforts her after the priest’s abuse. In the end, it is these two who go off into the sunset together, money in tow, to live happily ever after… maybe? Kind of? Honestly, I don’t really get what happens in the end.