I guess Hikari got turned into a doll, since there's the horror tag? Either that, or Ai has some sort of mental disorder where she thought Hikari, her new doll, was an actual person. Since she seemed to think all of her dolls were talking to her, that's not impossible, but I'm guessing they're all girls-turned-dolls. Well. Or it could be about a girl who's very good at playing pretend.