“Over New Year,” a 30-year-old woman tells Shukan Asahi (March 27), “I rented a hotel suite and spent the night there all by myself, drinking wine in a bubble bath and reading a magazine.” She smiles.

Is it a his-and-hers world when it comes to marrying, living single, living alone, or living apart from a romantic partner? What about initiating divorce or getting married more than once? We now know ...