The Second Wall - This was Phantom's second trial on his way to the Second Key, everyone knew this.
Obviously, by its very nature and name, a Phantom was supposed to pass the Second Wall after he overcame the First Wall.
But... one could never forget that there was neither the First Wall nor the Second Wall, just the Two Walls - only that was the challenge. They were part of the same entity that was critical at K2-Level.
The Two Walls was a powerful entity born not from the Phantom's energy like the Evolution Tree, but from its essence and its desires.
In a way, The Two Walls was the most accurate reflection of what the Phantom achieved, what it went through, what it wanted, and what kind of person it was on the inside.
In fact, very few Phantoms found themselves in a situation where the Two Walls began to interact with each other.
For this to happen, two simple but really difficult conditions had to be met.
