"I, Marken, vow upon my mana to listen to the teachings of my 'teacher,' Eadwulf, and use them in the unprecedented future that has yet to unfold" Ken took a vow, in his own simple terms, but Eadwulf, whom his vow was centred at, realised what those words indirectly voiced.
Eadwulf wasn't his 'master,' who would be a part of his life, but rather a teacher who would eventually be left behind after being learnt of the things he had to teach.
"Heh, a teacher, he said…." Eadwulf mumbled as he glanced down and shook his head. While a master-disciple relationship linked a pair of lives together for life, a teacher was only a teacher until he had something to teach his student, that was the understanding Eadwulf had over the matter in concern.
Now,
It was Eadwulf's turn.