Within the painting.
The Sword Immortal's sword movements appeared to lack any particular method or threat, seemingly just a sword dance meant for visual appreciation.
However, as Netherworld King's Sword Dao realm continuously advanced, he began to perceive the profound mysteries hidden within the dance.
Just as seeing a mountain is merely seeing a mountain, and seeing water is merely seeing water.
When Netherworld King first saw the Sword Immortal Sword Dance depicted in the painting, he was at this realm.
Seeing the sword dance simply as a sword dance, without uncovering any deeper mystery, and merely influenced by the immense Sword Rhythm within the painting to break through.
As his realm improved and reached the level of Tao Rule of Sword, Netherworld King revisited the painting and realized that it no longer seemed the same.
Thus, he had reached the realm where seeing a mountain is no longer seeing a mountain, and seeing water is no longer seeing water.
