The announcement trailer gave us previews for the rest of Roselia's trained art + costumes, but who could be who? Here's what I think.
First up, the costume representing Beatrice. Very simple, this is Ako. A small (and often perceived as younger) girl fits perfectly for Ako, the youngest and smallest of all Garupa characters. Plus, you can see a tuft of purple hair on the top. Definitely Ako's.
Second, the costume representing Felt. Also easy, this is Lisa. I could say something about the pose, but you can see her hair and glossed lips.
Lastly, you get to Rem and Ram. These ones are way harder to judge from image alone, but I believe Rinko will be Rem and Sayo will be Ram, for two reasons. One: The personalities of both match well. Two: Rinko hasn't had a Limited 4☆, and these costumes are coming from the most prominent females from Re:Zero, at least from the first half (which totals to 5 main girls anyway, if my memory isn't screwing with me). Emilia (who is Yukina) and Rem (who, I think, is Rinko) are the two main female characters in Re:Zero. Why wouldn't you have the 4☆ Gacha cards be them? No, Rinko not having a Limited 4☆ doesn't inherently mean she is guaranteed one, but there are enough factors to believe that she will be one with Yukina.
There's no way Yukina isn't a Gacha 4☆. I refuse to believe that they wouldn't make her one.
There's my thoughts. What are yours?
Now, what attribute will this event be..? And is there a chance EN gets the event early, like how they got Persona early? Doubt it, but possible.
Edit: NOTICED SOMETHING NOTICED SOMETHING Rem has an earring with a jewel that matches Rinko's image colour while Ram has an earring jewel that matches Sayo's image colour. That pretty much confirms Rinko will be Rem and Sayo will be Ram.