I Could Never Tell My Wife… I Got My Mother-in-Law Pregnant. (Madonna)

The "I Can't Tell My Wife..." series (妻には口が裂けても言えません、義母さんを孕ませてしまったなんて…。) from Madonna studio focuses on forbidden family taboos. Each volume follows a married man who, during a hot spring trip with his wife and mother-in-law, finds himself drawn into a passionate and secretive relationship with his voluptuous mother-in-law, leading to overwhelming temptation and irreversible consequences he must hide from his wife. Known for its mature actresses and emotional drama, this long-running series explores lust, guilt, and the breakdown of marital boundaries in classic Madonna style.