Badgerguardsman said:
In Mass Effect 2 during Samara's loyalty side quest, you encounter her daughter Morinth. Basically an Alien succubus, if you don't select either the Paragon or Renegade speech options, Sheppard appears to begin falling under her sway.
For people who want to see this, here's a clip:
youtube.com/watch?v=97DA44zDct8 from 50 seconds in to 1:20. I found it pretty hot, and I'm disappointed it gets interrupted.
But, there's more if you side with her character. She has the ability to both mind-control/seduce people into serving her and the ability to mind-meld with others and absorb their souls. She tries to tempt you into mindmelding, saying "My lovers spent their last moments experiencing pleasure you can't imagine. Like Nef--she died because her nervous system overloaded with an ecstasy so great she couldn't handle it. I want to give you that, Shephard. I want you to feel every nerve in your body pulsing with pleasure."
If you give in to her temptation, she does just that and kills you with the pleasure. It's definitely erotic. Here's a clip with female Shephard, 9:30 to end of video:
youtube.com/watch?v=I_O1gdKzJoYThe same thing with male Shephard isn't as erotic, but here's the clip in case anyone would prefer malesub, 10:50 to end of video:
youtube.com/watch?v=PMw4tKHndTY