Nemutan doesn’t really have a leg. She’s a stuffed pillowcase — a 2-D depiction of a character, Nemu, from an X-rated version of a PC video game called Da Capo, printed on synthetic fabric. In the game, which is less a game than an interactive visual novel about a schoolyard romance, Nemu is the loudmouthed little sister of the main character, whom she calls nisan, or “big brother,” a nickname Nisan adopted as his own when he met Nemu. When I joined the couple for lunch at their favorite all-you-can-eat salad bar in the Tokyo suburb of Hachioji, he insisted on being called only by this new nickname, addressing his body-pillow girlfriend using the suffix “tan” to show how much he adored her. Nemutan is 10, maybe 12 years old and wears a little blue bikini and gold ribbons in her hair. Nisan knows she’s not real, but that hasn’t stopped him from loving her just the same. “Of course she’s my girlfriend,” he said, widening his eyes as if shocked by the question. “I have real feelings for her.”…

According to many who study the phenomenon, the rise of 2-D love can be attributed in part to the difficulty many young Japanese have in navigating modern romantic life. According to a government survey, more than a quarter of men and women between the ages of 30 and 34 are virgins; 50 percent of men and women in Japan do not have friends of the opposite sex. One of the biggest best sellers in the country last year was “Health and Physical Education for Over Thirty,” a six-chapter, manga-illustrated guidebook that holds the reader’s hand from the first meeting to sex to marriage.