Okay, here is some suggestions then:

1: If they are going to be kept, they need a place to stay, I imagine a closet or a room where your OC goes to pick a girl to use.
An idea to keeping them there is to hang them in the air with their hands chained, with tubes attached to their mouth, vagina and butthole, that way, as if there's an automated maintenance to keep them fed and dispose any waste.
Show at least 3 of them in this position to show that they are all in the same position whenever they are not being used, though might be asking too much, but to show everyone on the list in that position together.

2.
A guro idea:
Cherry popping, these girls are likely virgins when abducted so maybe an aftermath of their first time, with blood and cum coming out of their vagina.

3.
Your OC dragging an unconscious girl by the leg, already done having sex with her.

One more thing: since this is posted on a Guro, website, can our suggestions include killing the girls and/or methods where the girl will ends up dead as a result?