AIKa Zero

Aika, now 19 years old, investigates a series of mysterious abductions at an all-girls academy. The abductions seem to target the most popular and attractive students, who are then taken by a mysterious entity that uses some kind of coercion to take control. Aika's interest is piqued when she witnesses one of these incidents, and she's approached by her former partners from R-16, who are also looking into the matter.