In refining the Eternal Night Thunder Sword, Yan Zhaoge encountered more difficulty than he had expected.
This actually made Yan Zhaoge feel a bit happier, because it correspondingly meant that this treasure was even more powerful than he had expected.
Lin Zhou had wielded this weapon with all of his might to great effect, but it was limited by the strength of the wielder and therefore could not display all of its power.
Using the Eternal Night Thunder Sword had put a huge burden of Lin Zhou every time he tried to stimulate the Thunder of Eternal Night. Stimulating a power which was of such a high grade caused a backlash against his own body.
Of course, this sword also brought great benefits to Lin Zhou, just like when Yan Zhaoge had managed to secure the Eye of the Thunder Emperor fragment and merge it with his right eye. Lin Zhou was in a similar situation with his sword.