The scientifically advanced Strangers of "Grenada" threaten to destroy our planet.
Justice heroine Hatsune Shindo, a.k.a. Prism Reica, gives her body and soul to protect humanity.
She has a younger sister: Hikari Shindo, a.k.a. Prism Shine.

Shine thinks the world of Reica. When Damned, the leader of Grenada, takes Reica hostage Shine breaks straight into enemy headquarters, and into unbelievable misery......!
Like her sister before her, the noble but naive imouto is transformed into a raving sexpot by the same mad scientist, Dr. Brain, who warped Reica into a mindless mesu.

Can Shine save Reica, or herself, from the infinite plunge into an XXX abyss?

[From DLsite English]