For your information, in order, the following characters appear in this promotional trailer:

  • Tighnari
  • Collei
  • Alhaitham
  • Traveler – Aether
  • Paimon
  • Dori
  • Cyno
  • Dehya
  • Nilou
  • Nahida

I would expect that many of these characters – excluding the Traveler and Paimon of course – will become playable characters in future updates.