Interpersonal rehabilitation games, which allow patients to compete or cooperate with other patients or unimpaired loved ones, have demonstrated promising short-term results, but have not yet been tested in longer-term studies. This paper thus presents a preliminary 9-session evaluation of interpersonal rehabilitation games for post-stroke arm exercise. Two pairs of stroke survivors were provided with a system that included one competitive and one cooperative rehabilitation game, and exercised with it for 9 sessions in addition to their conventional therapy. They were able to choose the game they wanted to play in each session, and had to exercise for at least 10 minutes per session. Both pairs completed the protocol without any issues, reporting high levels of motivation and consistent levels of exercise intensity (measured using inertial sensors) across the sessions. Furthermore, the maximum difficulty levels reached in the cooperative game increased over time, and improvements of 1-8 points were observed on the Box and Block test. These results indicate that 2 different interpersonal games are sufficient to promote high levels of motivation and exercise intensity for 9 sessions performed over a 3-week period. As the next step, our system will be expanded with additional competitive, cooperative and single-player games, then tested in full clinical trials in both clinical and home environments.