Yeah, "unique", in the context of this game, usually means an idol that only shows up once .
All idols have sexual preferences, and romantic success also depends of your friendship level with the idol. If she's constantly rejecting you, it's either because your friendship level with her isn't high enough, or because her sexual orientation does not include your gender. Keep in mind that rejection can also happen if the idol has the Asexual trait, or if she's already in a relationship.
Ahh got it. Also, how does it work with multiple idols? Are you able to hit romance lv 5 with as many as you want? If there's a cap, is there a way to lower your love level with idols to move to a different one?
Is there a way to prevent idols from graduating so I don't lose any unique idols? Sorry for the questions, I just got this game and I'm very curious about the mechanic's specifics!
I believe you can, in theory, reach lv. 5 romance by flirting with any +18 idol as long as they're interested in the player's gender, aren't currently dating and don't have the Asexual trait, though you can only date one idol at a time. I'm not sure how you'd go about lowering romance levels, though.
As for graduating idols: you have the option to convince them to stay a little while longer in the group by dragging them to your office and selecting the appropriate dialogue choice (don't remember which one it is). Depending on how much influence you have over them (and a few other variables such as salary satisfaction, perhaps), they might be willing to postpone their graduation. Otherwise, base idol graduation date depends on how happy they are in the group overall (no depression/injuries, good salary, no bullying, etc.)
