Gender roles in dating
Male-to-female transformations tend to vastly outnumber the opposite when this trope is in play. It might be Played for Laughs, Played for Drama, or even played for horror if Loss of Identity or an unusual amount of Squick is involved.
For Laws related to this trope, see the First Law of Gender-Bending, the Second Law of Gender Bending, and the Third Law of Gender Bending.
When a man retires, he sometimes becomes trapped in a family he doesn't know, with nothing to do, and he tends to die soon after from his sudden lack of purpose.
I am not an expert in this topic; however, maybe I can provide some insight into Japanese culture and its reflection in manga, as well as some recent trends in manga.
Despite its technological advancement, Japan somehow manages to retain much of its historical character, in addition to blending in the overwhelming influences of the West.
Truth in Television to some degree, as the ratio of real life trans women to trans men is roughly 3:1, but the ratio in fiction is still a much higher number. Bland: Women have appreciably higher pain thresholds than men.
Some of Japan's greatest literary figures were women, such as the novelist Lady Murasaki, who lived about a thousand years ago. However, when Japan became war-oriented and feudal, women quickly became second-class citizens.
Most women were treated as they have been treated throughout history: as merchandise, or servants, and as heir-producing machines.
For this trope's impact on relationships, see Unsettling Gender Reveal, Jumping the Gender Barrier and Gender-Bender Friendship.
Contrast with Transsexual and Hermaphrodite, which are real-life phenomena (though on rare occasions, a Gender Bender character might a hermaphrodite instead of, strictly speaking, the "opposite sex"; also, Gender Bender stories can intersect with transsexual characters, by having someone transition unexpectedly by magic, or have the experience of being gender-changed bring a transsexual character out of denial.