Karen starts as an ally to Win Kirifuda but betrays him by aligning with Prince Kaiser during their conflict, actively assisting Kaiser against Win—including an incident where Kaiser throws her into a hole as part of their confrontation. She later rejoins Win's group, becoming a core member of the Duema Saikou Club at Maihama Academy, which Win establishes to promote enjoyment of Duel Masters. This return shifts her from an antagonistic role to a supportive position within Win's circle during the Duel Wars tournament arc. Her character arc transitions from opposing Win to competing alongside his team in the Duel Wars, aiming to prove their strength at the academy. Karen stands among the "old faces" reuniting with the club, alongside Kendra, Masugi, and later Bowie.