Touko and Kakeru are basically one person, who has aspects spread out through space and time. This is evidenced by all the other versions of Kakeru that can be seen when Kakeru is alone in that clearing. The thing that makes Touko special is that she's a female variety, which is perhaps the reason she can interact with Kakeru physically, which is not possible for the male manifestations (and which means there might be a Yin/Yang theme going on). Sparkly things enable Touko to see events occurring in other worlds, and are not necessarily her own future.
The main hint for this ideas occurs during episode 12, where Touko and Kakeru's roles are mostly reversed, with Touko being the outsider and Kakeru being the who already lives in that town. Scenes likes probably play out all the time throughout various alternative worlds. It is possible that Touko will be able to keep on seeing Kakeru or his other manifestations after Kakeru leaves town, indicated by how she can still hear his voice.