They'll show up soon. After this fight with the demons. The rude ass dude who passed the demon hunter exam is also another party member of their later on down the road. The boar dude ended up becoming a demon hunter just because he follows the strong and met demon hunters. You did see the blond hair dude already, he was at the end of the exam saying he'll die anyways even though he passed.
Considering next episode is a fight, not until 10 or later at least. I'm surprised how early they spoiled the relevance of these characters via the opening and ending credits when the show is 26 episodes long and we won't be seeing them for this long. 1 second cameos would have been fine, and maybe much more inclusion in the next opening and ending song.
Yea, makes more sense to get them appear in either a new opening when the 2nd cour starts, or changing the visuals of the current Opening if they decide to let this OP and ED run for all the 26 episodes. But well, at the other side, something to look forward to!