Secret Orders After School -The Undercover Operation-

Mariko Kitahara arrives at St. Dominic Academy to find her long-lost sister. She vows to end their separation and live together like they used to. However, what awaits her is an unruly student, Arisa, seducing other students in the literature club and doing as she pleases. There are also members of the staff who are very interested in "training" Mariko and taking advantage of her quest. What will happen when the handsome but cruel board chairman discovers her true identity?

(Source: Renta!)