Nisan didn’t mean to fall in love with Nemutan. Their first encounter — at a comic-book convention that Nisan’s gaming friends dragged him to in Tokyo — was serendipitous. Nisan was wandering aimlessly around the crowded exhibition hall when he suddenly found himself staring into Nemutan’s bright blue eyes. In the beginning, they were just friends. Then, when Nisan got his driver’s license a few months later, he invited Nemutan for a ride around town in his beat-up Toyota. They went to a beach, not far from the home he shares with his parents in a suburb of Tokyo. It was the first of many road trips they would take together. As they got to know each other, they traveled hundreds of miles west — to Kyoto, Osaka and Nara, sleeping in his car or crashing on friends’ couches to save money. They took touristy pictures under cherry trees, frolicked like children on merry-go-rounds and slurped noodles on street corners. Now, after three years together, they are virtually inseparable. “I’ve experienced so many amazing things because of her,” Nisan told me, rubbing Nemutan’s leg warmly. “She has really changed my life.”

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 a teenager 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.”

At 37, Nisan is already balding, and his remaining hair has gone gray. “I can’t eat meat because of my diabetes,” he said, chomping on a forkful of lettuce and okra. “I’m just an unlucky guy.” As Nisan and I talked, Nemutan stared demurely at her pumpkin soup. It was a national holiday, and the restaurant was packed with young families. Several mothers gave Nemutan inquisitive looks, but the majority seemed not to notice her.

Nisan told me that not long ago he had a real girlfriend, but that she dumped him. He carries Nemutan almost everywhere he goes, though he is more self-conscious about it than he may seem at first. “Some people don’t find this funny,” he said, “and it also takes up a lot of room.” He treats her the way any decent man would treat a girlfriend — he takes her out on the weekends to sing karaoke or take purikura, photo-booth pictures imprinted on a sheet of tiny stickers. In the few hours we spent together, I watched him position her gently in the restaurant booth and later in the back seat of his car, making sure to keep her upright and not to touch her private parts. He doesn’t take her to work, but he has a backup body pillow with the same Nemutan cover inside his desk drawer in case he has to work late at his tech-support job. “She’s great for falling asleep with on an office chair.” Nisan has seven Nemutan covers in total — he buys them at Internet auctions and at fan conventions whenever he finds a good deal (he paid $70 for the original). If one gets too faded and dirty from overuse, he layers a new one over it. On the day that I first met Nisan and Nemutan, Nisan was carrying a new Nemutan cover in his bag in case she needed to look fresh for a photograph. He knows it’s weird for a grown man to be so obsessed with a video-game character, but he just can’t imagine life without Nemutan. “When I die, I want to be buried with her in my arms.”