Shen Yue's circumstances have been ever-changing; he has experienced many bizarre and incredible things, from the Bright Realm to the Dark Realm, and then eight hundred years ago...
But Shen Yue remained unchanged, so when Nuanyu, Ishida Hideko, and Ye Xuan'er reunited with him after a long separation, they felt no unfamiliarity.
They believed Shen Yue should be like this.
But how can a person remain unchanged unless they are in an eternal state, just like pure gold, which remains pure gold whether buried underground or in the mundane world.
Shen Yue seemed to understand everyone's doubts and spoke slowly, "The 'Tao Te Ching' begins by saying that the Tao that can be told is not the eternal Tao."
