Siliconera sheds some light on the elusive plotline of Hiiro no Kakera: "Hiiro no Kakera DS starts with quite a bit of exposition. It begins with a detailed explanation of why our heroine, Tamaki Kasuga, is suddenly living with her grandmother in a rural mountain town. (Her parents decided to focus on their careers and ditch her.)
So Tamaki's making the best of it in the prologue, wandering around and enjoying the ambiance. All of a sudden she's assaulted by three slimy, one-eyed, purple ooze monsters. She's then quickly grabbed from behind by the attractive Takuma, who proceeds to defend and save her."