The first time they came across Basen was about two weeks after they had destroyed the Ona clan.
They had already left the kingdom they had entered after the Empire, using the fastest possible route that led them straight through it and into the next kingdom, which was also one that was slightly hostile to the Alastar Empire.
It was during their journey there that Basen Alastar appeared.
They had a feeling that he wouldn't let them get away easily, which was why they tried their best to get as far away from the empire as quickly as they could, only for the powerful foe to still catch up to them.
It happened during the night, which was one of the reasons they were able to actually survive.
Nicholas, Lyle, and the servants were resting in a forest, with Ruby getting further away from them as she was about to start the evolution process and reach the Grand Knight realm.