If you go into Olivia's house in Sun/Moon, she has a lot of Stufful dolls that are "really popular among single women". She also has an actual Stufful among her collection.

So what if one night, Olivia feels mighty lonely and decides to grab one of her dolls for some "company", only to pick up her pet Stufful instead? Maybe she's a bit surprised at first, but the more she thinks about it, the more her curiosity gets to her.