After absorbing the Thunder Energy of the Fourth Layer, Lin Xin evidently felt that his body could hardly bear it anymore.
In the Rushing Thunder Sword technique, after absorbing Thunder Energy from each layer, there was always a rather lengthy adaptation process, which essentially was the process of Thunder Energy continuously tempering the body strength of the cultivator.
Lin Xin was now certain that the One Hundred and Eight Forms of the Rushing Thunder Sword was at least a top-tier Sword Technique of the True Monarch Level, but its cultivation difficulty was tremendously high.
The First Layer alone required a common person five years, the Second Layer according to the records theoretically required ten years, the Third Layer fifteen years, and the Fourth Layer twenty years.