If an adult of sound mind consents to sex with me and they're not under duress, that's not rape.
A person does not have to want to have sex to consent to sex. A sexual relationship can be horribly exploitative and even abusive without rape being involved.
Thank you for clarifying what I was trying to get at. To be clear- the player is not explicitly or even implicitly coercing the other person into sex by threatening consequenes if the person does not consent. In fact, sex does not even need to be done at all- the player could aggressively flirt and bed, or just flirt. The point is that the LI will accept them regardless.
The twist or complication is that the partner perceives an issue, even if/when it is not there. If you were to ask them (him or her) if they are willing, they would explicitly say 'yes' (because they fear what would happen if they said no,). It would be the point at which they would be comfortable in saying no, and realize that they aren't being coerced, that the emotional relationship would actually begin.
If they believe there will be negative consequences to turning down sex with someone, it's difficult to say they've given their consent either though. It's possible that the solicitor is not even aware of the implications of their actions (though one could argue they should've taken their relative statuses into account before soliciting the person in question) and has no intention of coercing/forcing them, but the solicitee won't necessarily know that. It's a complex situation.
The complexity is the point here.
It's not like the dynamic couldn't be perceived to exist in other Bioware games. In Mass Effect, Commander Shepard is a superior officer, authority figure, crack special forces, one of the most deadly people in the planet with a body count that measures in the battalions, and is explicitly above the law for any retributive actions he or she might feel inclined to for any grievance what so ever.
Whether your Shepard would or not, any of the LI's would have grounds to feel coerced if they were inclined to. They don't, but not because the subject of non-explicit coercion could never be raised when an unaccountable military commander starts flirting with someone already in a subordinate relationship.
In canon, Liara was perfectly willing and actively interested in Shepard, even if Shepard wasn't. But consider how different it would actually have to be had Liara been afraid that, if she wasn't useful and pleasant to be around, that she might be kicked off the Normandy and back in the sights of Saren's assassins?