Yukkuri Panic: Escalation

Dating Simulator by Rolling Star.

Rie Komatsuzaki has just transferred to the prestigious St. Yale Academy, a Catholic school for girls, but it's not her choice. After finding her mother romancing her private home tutor, she is now forced to attend this boarding school to keep the incident secret. Sad and confused, she finds herself alone and without friends. Looking for some peace from all her troubles, she enters the school chapel. Within the holy sanctuary, she encounters Naomi and Midori making love. She's immediately taken aback -- “What are they doing? Girls aren't supposed to touch each other like that!” Yet, she can't find the willpower to look away, and a warmth fills her panties as they grow increasingly wet. Before she knows what's happening, she's become the new plaything for the two girls as they teach her about the wonders of sex.