Quite simply. As each character sends you an email about a possible meet-up (which can be read from the private terminal in the Personal Apartment), you either invite them up or go out onto the Silversun Strip to meet them, depending on the character. You will have to complete the characters' relevant content in the main game before their Citadel-specific content will become available; for example, you'll have to complete Priority: Rannoch before you can invite Tali up, or Priority: Horizon to invite Miranda. Terminator-HIX
But when I go on the terminal, there are only emails from certain people. On my first playthrough I could invite EDI, Ja,es and Tali up but on my second Tali was replaced by Liara. Do they pop up later or am I going to have to replay again? 220.127.116.11
^ They pop up later. You don't get to invite them up one after another. There is an initial batch of mail, then you go out to meet the corresponding characters on the Strip (as with Ashley and Garrus, for example), or invite them to the apartment for a dialogue (as with Miranda and Liara, say).
When that's done there will be more emails. Do those characters as well, and so on.
Bear in mind that some characters depart from the pattern. In the case of Kasumi, for example, there is no email. You actually have to examine a peculiar artifact on the end of a partition in the Casino, at which point by coincidence Kasumi enters with a team planning a heist, spots Shepard, and tries to back out ("Whoops, wrong casino"). In the case of Miranda, you do get an email to meet her in the casino (she will be wearing a red dress). Also you can invite her to the apartment. SDoradus (talk)
Thanks alot for that. Just did some missions and unlocked some more emails. 18.104.22.168
Good to hear. A quick note on romances. I've been trying to definitively list all the options. You will wake up at the end of the party and watch your current love interest wake up beside you. ("Look who's here"). This is particularly true of Miranda and Liara. If there is no romance, you wake up alone of course.
- Possible exception: According to LilyHeartsLiara, if there is no other romance going on you can get a tender scene with Samara, but I have not seen it yet.
- Definite exception: even if you romanced Kelly and none other, triggering the paramour achievement and displaying her framed image in Shepard's Normandy cabin, you can't invite her to the party; therefore you can't watch her wake up.
That last would be because she's clearly not a sufficiently important character. That is shown in the endgame also. Kelly is the only former associate or romance you can't get in touch with before the London battle - probably because by that time she would have been harvested along with her refugees.
Nonetheless, I was a little surprised, given that Traynor made it. Joker did mention her during Thane's memorial, so she wasn't completely forgotten. Perhaps the voice actress had other committments, or she didn't fit the storyline - not a superstar spectre, alien, biotic goddess, no kind of warrior or genius, unlike Traynor. Nothing unusual about her at all. SDoradus (talk)