I've been thinking about why my gut says Luna might be the first girl to get a full sex scene outside Eternum and I think most people's reasons why she wouldn't be, are the reason I think she will.
She has lived her whole life without even being able to touch people. The first time she touched Orion she got super handsy and had to pull back, I could easily see her pushing her desire to feel all of him into a handjob and then that just going forward from there into a full sex scene.
I also don't think she's as naturally introverted as she seems, I think she just got forced into that kind of life by her powers. I mean, look at her jokes and humor and the way she acts in Eternum versus outside the game. Also, not to mention that sometimes the most introverted girls are also sometimes the biggest freaks in private.
And they already held hands in the Warthog server so... they're practically married, what's a little p-in-v after that?
I do think Annie is the more likely one, after her Nova would be a close contender. I just like to speculate and stuff.