Risako Nagisa (凪紗 りさこ Nagisa Risako) 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 in school, she dresses relatively conservative, outside the school she prefers skimpy clothes like Neena Hagen. In AIKa Zero, Risako wears a lab coat due to her undercover role as a school nurse.
AIKa R-16:Virgin Mission Edit
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 makes a loud moan and her voluptuous body crumbles to the ground unconscious. There, Karen partially removes her skimpy bathing suit to reveal a transmitter, Risako's trump card. Without any chances of now receiving any help, and thus being no threat, Risako's body is carried by Gusto Turbulence to the ship, where she is left with the other captives in the deposit, restrained by several belts in such a way she can hardly even move. We can assume she remains like this for the days it takes for the mission to be over, probably taken care of, in her practically immobile state, by the ship's crew.
Risako has combat skill comparable to a 16-year-old Aika Sumeragi and even gained the upper hand until Karen Minamino's interference. Although Risako was likely stronger than Aika at this point, getting completely overwhelmed and knocked out despite being in a dominant position because of a hot crab likely implies that the gap between the two wasn't massive.
In Aika Zero, Aika seems to have completely surpassed Risako as Miyu was able to instantly take her out with overwhelming speed while Aika seemed to have little trouble with Miyu. This is further shown when Risako was seen on the ground and forced to use a gun for the time in the series against Misumi while Aika was able to take down multiple White Knights with relative ease. Although the battle between Misumi and Risako isn't shown, given her position on the ground and the fact that she sighed after resorting to using firearms in battle for the first time in the series, it's likely that Risako was outmatched in a battle of pure hand-to-hand combat.
- The name Risako means "lovely" (麗), "village" (里), "white jasmine" (莉), "pear" (梨) or "reason, logic" (理) (ri), "help" (佐), "sand" (沙), "thread, silk" (紗) or "already, now" (早) (sa) and "child" (子) (ko).
- Risako's surname Nagisa means "beach, shore" (渚).
- Risako has the largest breast in the R-16 and Zero series