The Blade King slowly approaches that place. He can feel the barrier through using the spiritual vision technique. Well, normally nobody would be able to see that area if he did not use spiritual vision or similar techniques like that.
Blade King all the time uses the spiritual vision while he approaches that place and he can already see that barrier. Naturally he did not break the barrier or do something. Well if you are wondering why he became sure that this is the Sam who is inside of that barrier, then it is because Sam previously told him he has a barrier like this that could prevent any Monster or Warrior from approaching his place.
Also if anyone tries to break that barrier they won't be able to do that until that person does not reach the legendary grade. Sam, even though wasn't sure if anything like this would happen or not, he still prepared himself and because of this he already informed the human king and the Blade King about this.
