A third-year student of L'Ecole des Cinq Lumières and the Student Council President. At first she thinks the Pretty Cure thing is a farce, but was forced to believe it when the Nightmare invaded her house. But then she failed to become a Pretty Cure due to her 'do-things-herself' mindset. Despite so, Nozomi continued to bug her about becoming a Pretty Cure, and after realizing that she wants to protect her friends, Karen is able to become Cure Aqua. During the course of the series, she develops a rapport with Milk and discovers her dream to help those who are sick, and she starts learning on how to become a doctor.