Zettai Kangoku

Spy soldier "Grave" investigates the facility of a female prison where human experiments are being performed.
With extensive cosmetic surgery and a disguise, Grave becomes a warden of the prison.
Inside he discovers countless young girls being sexually abused by another warden named Eliza.
Among the prisoners is Anna, Grave's wife, who doesn't realize who's here to save her.

[From DLSite English]