I am Risako Nagisa is a teacher of the school Aika attends who first appears in AIKa R-16: Virgin Mission. In AIKa R-16: Virgin Mission, Risako has multiple outfits. While at school, she dresses relatively conservative while outside she prefers exclusively revealing and skimpy clothes, in a manner similar to Neena Hagen. In fact, we only see her wearing bikinis of two different types and then a full set of lingerie ever since the trip with the Treasure Hunting Club begins. In AIKa Zero, Risako wears mostly a lab coat due to her undercover role as a school nurse.

Risako is a very attractive and voluptuous women, with wide hips and particularly enormous breasts, as well as a very dangerous foe, with fighting capabilities that can even match Aika. Using her astounding looks and sensuality as a standard way of getting what she needs, she has all the characteristics of a femme fatale. Risako is also the adviser of Treasure Hunting Club. She turns out to be an enemy, having controlled three of the students with electronic devices to attack Aika Sumeragi and Eri Shinkai and also tried to take Karen away. Her true identity is an agent from a mysterious organization sent to observe Karen. With help from Karen Minamino, Aika Sumeragi manages to defeat Risako in episode 2, Peach Peach Beach, still having quite some troubles and finding her a very difficult foe. Once she is beaten, her hands and feet are hastily tied to keep her under control. Still defiant and apparently unmoved by her defeat, Risako refuses to give any information, warns them to stop in their quest and tells them they are being overheard and reinforcements for her will soon arrive. Her arrogant attitude is cut short, however, when Karen unexpectedly pulls a gun on her and unceremoniously shoots her with a tranquilizer dart from short range. Risako then lets out a loud moan, her face blushing furiously and quickly changing to a never seen before expression of anguish and shock, as the tranquilizer dart penetrates her voluptuous body