Once Alex had gone through the 37 elemental Daos, he had to go through the few remaining ones that were either elemental-adjacent, or simply didn't have anything to do with the elements at all.
He produced an aura belonging to his Dao of Plant Growth, which the artifact accepted immediately as the 38th Dao. It had been one of the first Daos he had learned, but ever since Whisker had learned it as well, Alex hadn't had the need to make use of it, so it had been a little wasted for the past few centuries.
The next aura he produced was for the Dao of Five Elemental Interaction. He had long since moved past this Dao to learn a better version of it, but that didn't mean that it wasn't a valid Dao.
After the artifact accepted it, Alex used the Dao of Seven Elemental Interaction, which was the better and slightly different version of the previous Dao. That made a total of 40 Daos, and Alex had already moved past that one as well.
