After stem-cell transplantation, pediatric patients must remain in aftercare due to a high risk of suffering from a plethora of life-threatening organic problems. In this phase, communication with the clinicians is key for an increased survival probability. The multidisciplinary INTERACCT aims at developing a child friendly communication tool based on gamification principles in order to foster this important communication. Additionally, INTERACCT should stimulate exercises and treatment compliance. Finally, through analyzing gaming scores, INTERACCT should also act as a sensor for detecting problematic phases children are going through. Since the design of INTERACCT is key to its success, we present results from our user-centric and participative design approach using methods from design thinking and explorative design with school children aged 8-14. The results are game characters and story lines, which will inspire the game design of the INTERACCT computer games.