This one's technically one of the very last extras before the serialization started, as you can tell by Natalia being way more aloof, but I thought it captured the spirit of these two adventuring together and was a nice starting point.
Extras won't be coming in any kind of chronological order, so you're going to have to do some guesswork between the art style, their adventurers outfits, Natalia's haircut, them calling each other by their names, etc.