Self-care systems shift responsibility to patients which require prudence and motivation. Data visualizations of performance in rehabilitation games support patient motivation, but health numeracy pose barrier to interpretation. This paper contributes a case study of how one therapist used storytelling to aid 14 patients in understanding timeline and heat map visualizations, provided by a co-designed tablet game. The therapist's verbal storytelling catered to patients' level of self-awareness while she used pointing gestures to draw patient attention to the visualizations. Patients with no awareness did not link performance to their injury, which resulted in distrust in the therapist-provided training. The study presents guidelines for designing visualizations in self-care systems targeted to stroke patients in clinical and home contexts.