The Celestial Capital Soundless Thunder Sword transforms the Supreme Yang Fierce Thunder into Ultimate Yin and Soft. This Yin Yang Transformation is extremely intricate, and was created by the flash of inspiration from the Celestial Fool, resulting in such a profound mysterious technique.

However, ultimately, Celestial Fool lacked depth and sufficient wisdom. He created the Celestial Capital Soundless Thunder Sword, but couldn't truly perfect it even after thousands of years.

Moreover, Celestial Fool did not realize that the most important issue was achieving the Yin Yang Transformation of external power.

Gao Xuan obtained the Celestial Capital Soundless Thunder Sword from Celestial Fool and immediately grasped the key to this Secret Technique.

Although Gao Xuan did not have the Formless Sword to depend on, his Divine Soul contained the Yin Yang Five Elements Rune Seed deep within.

The Formless Sword's transformations ultimately can be achieved with magic. Gao Xuan used the Formless Nine Revolutions Inference to deduce the transformations within, breaking through the original limitations of the Secret Technique.

The Celestial Capital Soundless Thunder Sword was originally just an offensive secret technique, extremely powerful. After Gao Xuan's improvements, it was able to convert external power into one's own power.

Although this transformation had many limitations, it truly expanded the application range of the Secret Technique and essentially enhanced the technique's level.

Celestial Fool had lived for over six thousand years and had considerable insight. He had delved deeply into the Celestial Capital Soundless Thunder Sword, and after Gao Xuan's guidance, he suddenly comprehended it, greatly increasing his Dao practice.

The Yin Yang Transformation of the Celestial Capital Soundless Thunder Sword is particularly adept at transforming Thunder Power. With such intricate changes, passing the Thunder Tribulation is not difficult.

For cultivators, the Thunder Tribulation is the most lethal and terrifying obstacle.

Being able to face the Thunder Tribulation calmly makes the path to eternal life very smooth.

Celestial Fool does not dare to say that he can directly reach Earth Immortal, but achieving the Ninth Layer of Human Immortal is unquestionably attainable.

Gao Xuan's guidance on the Secret Technique not only helps him pass the Ascension Tribulation but also points out a path to the Path of Eternal Life. A person of Celestial Fool's age couldn't help but get excited and immediately swore an oath to forever remember Gao Xuan's great kindness.

Gao Xuan did not take such words seriously. Although immortals have long lifespans, the time of an everlasting world is too lengthy.

Gao Xuan helped Celestial Fool up, saying, "Friend, there's no need for this. I also learned a superior secret technique from you, mutual benefit."

Celestial Fool promptly said, "It's not the same, Celestial Master's guidance is the supreme Dao, disciples are deeply moved…"

"The road of cultivation is long, only with tireless exploration day and night can one reach the true path..."

Gao Xuan encouraged Celestial Fool with a couple of sentences, then changed the subject, "Ling Ji's Dao practice is shallow, please bother yourself to guard here. I'll go down to have a look. If there are any changes, just protect Ling Ji and leave first..."

Guarding Ling Ji is a small matter, Celestial Fool naturally agreed heartily.

Gao Xuan's divine techniques surpass them tenfold, even a hundredfold, going down with him would only be a burden. Gao Xuan going alone is better.

Gao Xuan instructed Ling Ji a couple more sentences, Ling Ji wanted to follow Gao Xuan but didn't dare defy his words, only reluctantly nodding.

With everything arranged, Gao Xuan then proceeded independently downward.

After the twentieth layer, no trace of cultivators was seen. The number of demons on each layer also quickly increased. The level of power in demons also kept getting higher.

With so many demons, Gao Xuan didn't want to waste time on little demons and avoided them whenever possible, only attacking and killing demons when he couldn't avoid them.

Thus proceeding downward for more than two hours, Gao Xuan reached the seventy-seventh layer.

This layer of the cavern stretched over hundreds of thousands of miles, and the dense Ultimate Yin Filthy Qi sprawled everywhere like black clouds.

Gao Xuan felt an intense chill, fortunately, his Primordial Unity level was too high, and his Primordial Cross-Training Golden Body was perfect and flawless. Despite the strength of the Ultimate Yin Filthy Qi, it couldn't penetrate the Primordial Golden Body.

Gao Xuan tried various magical artifacts on the way.

In comparison, the Celestial Dragon Eye had the weakest resistance against the Ultimate Yin Filthy Qi. Although it wouldn't be contaminated, its power would be restricted by the Ultimate Yin Filthy Qi.

Especially below the sixtieth layer, the external power of Celestial Dragon Eye was reduced by seventy percent.

The Jun Heaven Wheel's protective effect was the best, and the Primordial Magnetic Divine Light wouldn't be polluted by the Ultimate Yin Filthy Qi. However, it couldn't curb the Ultimate Yin Filthy Qi either.

As the Ultimate Yin Filthy Qi became more intense, powering the Jun Heaven Wheel required more energy.

The Eternal Celestial Dragon Claw, at this moment, played an important role. In terms of level, it was still inferior to the Celestial Dragon Eye.

However, the Great Mighty Celestial Dragon Seal and the Eternal Hell Seal of the Eternal Celestial Dragon Claw were too apt for dealing with filthy demons.

The Great Mighty Celestial Dragon Seal is fiercely powerful, plus it has a special demon-subduing force from the Buddhist Sect, making slaying cavern demons effortless.

The World-Ending True Flame was even more domineering. Under its flame, the Ultimate Yin Filthy Qi was like liquefied gas. As a single flame descended, the denser the demon qi, the hotter the flame burned.

The Eternal Hell Seal could absorb the Ultimate Yin Filthy Qi, thereby countering the cavern demons, worthy of being called using poison to overcome poison.

However, the Great Mighty Celestial Dragon Seal and the Eternal Hell Seal consumed a lot of power when activated. Faced with the endless cavern demons, these powerful Dharma Seals seemed overly thin.

Gao Xuan's Divine Soul Power was fierce, allowing him to wield the Eternal Celestial Dragon Claw for extended periods.

However, this efficiency was too low, and relying on the Eternal Celestial Dragon Claw couldn't possibly solve the problem of the Cave of Ten Thousand Demons.

Gao Xuan's speed in slaying demons couldn't keep up with the speed of demon reincarnation.

Gao Xuan discovered that the cavern became increasingly dangerous, and to conserve power, he decided to first refine the Five Elements Celestial Net Gauze Robe.

This light gauze robe was like water, gas, or light, capable of spontaneously adjusting its transformation with external power, truly marvelous for protection.

The little Yuan Buyin managed to block the Eternal Celestial Dragon Claw with the Five Elements Celestial Net Gauze Robe.