Niku Nie Seitokai ~Bishimai Kuppuku~

Akito Saotome (protagonist) lived with two Naomis: fiancee/class president Naomi Kitagawa, and obnoxious younger stepsister Naomi Saotome. One day the two Naomis took Akito on a date. With a beauty on each arm, Akito had some fun at the expense of a gang leader named Bob. Bob decided right there that these two girls would be the fruits of his revenge, and began to lay the groundwork for assault.

Stepsister Naomi is ravished physically, while fiancee/class president Naomi's heart is soiled!

In the end both Naomis succumb to pleasures and are indistinguishable from copulating sows.