It had been on a whim that Sebastian decided to go downstairs and check his mail -- something that he had rarely done since his time at Bellum, being more concerned with the supernatural elements and forgetting the normal day to day duties he still had to attend to. If he had his way, he would have been doing this alone, without running into anyone else in the lobby. Sebastian had become accustomed to being alone in the apartment, with everyone else knowing each other and having their own problems to deal with, and so he took it for granted that he would get his wish. By the time he noticed that there were two others at his destination, it was too late to turn back without looking either silly or rude.
Truthfully, social situations were not his forte, he never knew how to appear friendly without trying too hard, and usually came off as stand-offish. Sebastian kept his head down as he made his way to his own mailbox, hopefully not interrupting anything too important. He gave a friendly nod -- or, at least, he hoped it was friendly -- and a quick "hello" when he ended up next to them. He recognized Vlad, but only vaguely, and had never even seen or spoken with the girl.
Hopefully he was not seeming rude by not introducing himself. "Sorry," he murmured uncomfortably, feeling distinctly out of place in midst of their conversation. "I don't mean to interrupt." His nervousness was most certainly noticeable, as he fumbled with his keys and opening of the mailbox.