Within Feng Yingyue, an intense heat was rapidly rising from her loins into her Lower Dantian, it was boiling her Water Qi. But with the Fire Qi from her Middle Dantian, her Water Qi had no place to go to. As such, it condensed further and further under this oppressive heat. Already her Fire Qi and Water Qi were in conflict. But her Middle Dantian was almost fully crystallized already. Although no Qi could leave her Middle Dantian at this point, there was an abundance of Qi throughout her meridians and vessels. Most of this Qi was Fire Qi.
Feng Yingyue had so much heat in her Middle Dantian, it was becoming painful to her. Thankfully, the 'Soul-Steam Circulation' layer was not finished yet. As their Essence Fires had merged, Cao Yun and Feng Yingyue's meridians began to merge too. First of all, from their Huiyin, their Conception Vessels and Governor Vessels intertwined. As such, a large amount of Feng Yingyue's excess Fire Qi suddenly flowed within Cao Yun. It was being pulled by the influence of the Solar-Orchid Flame. In return, Cao Yun's body naturally sent more and more Water Qi within Feng Yingyue's Lower Dantian since his own Lower Dantian had a vast amount of it.
The two cultivators moved in new ways, with varying rhythms, instinctively following the flow of the elements within each other. It truly was like a dance, but neither cultivator was leading the dance, they were simply following the wheel of the five elements. Both of them were completely free now that they had, paradoxically, relinquished all control. Their actions and movements were all instinctive, in accordance with the Dao and nature itself. But at the same time, they were fully immersed in the moment and in all the sensations and feelings from one another. Cao Yun had no doubt about his relationship with Feng Yingyue because he wasn't thinking about anything but her dancing with him.
More and more meridians began to intertwine as their bodies melted into one another. The very first one was the Belt Vessel, Dai Mai, the only horizontal meridian in the human body. Its main purpose was to harmonize the flow of Qi through the other vessels and meridians. Now, there was only one Belt Vessel forming a lemniscate around the two cultivators as their navels and lower abdomens were in tight contact.
This was the main principle of 'Soul-Steam Circulation'. Now that their Dai Mai were connected, their other Extraordinary Vessels and standard meridians began to merge too. Soon, all of their meridians were forming only one large system. Besides, the cloud around them was also forming new meridians and vessels, fluid pathways between their two bodies.
At this stage, Feng Yingyue was benefiting more than Cao Yun. Indeed, her Lower Dantian was rapidly filled with Water Qi. In a matter of minutes, it became perfectly balanced with the Fire Qi in her Middle Dantian. Moreover, Cao Yun's Solar-Orchid Flame was also resonating with her Middle Dantian. It was extremely strange, but something deep within Feng Yingyue's blood and heart seemed to be connected with the Solar-Orchid Flame, or maybe with the Dao of Fire itself.
Suddenly, everything stopped for an instant. Feng Yingyue's embrace tightened as both of her Dantian were now fully crystallized. She had even more Fire Qi and Water Qi than before. At this very moment, she was a 7th-grade Mortal Warrior. Now, she had to make those two crystals collide and explode in order to finally produce her Soul Embryo. The merged Essence Fire was strengthening her body and the excess energy could flow into Cao Yun. As such, the strain on her system would be reduced, but she still had to be able to survive this reduced strain even though she had even more energy than before.
During this mere instant, Cao Yun and Feng Yingyue entered the third layer of 'Twin Flesh Furnaces, Soul Cauldron', 'Melting the Cauldrons'. Their physical bodies were merged, their meridians were merged, only their souls remained. As the Essence Fire was moving all around and within the two cultivators, it finally reached their Upper Dantian. This sudden pause was not just because of Feng Yingyue's crystallized Dantian. In fact, there was no pause at all. What happened was that their minds had suddenly been invaded by their own Essence Fire. For an instant, the entire world seemed to have paused around them. However, it was only their perception.
Their seas of consciousness began to merge as well. Above them both, a third sea of consciousness emerged. The water rose and rose. Within their souls, a gigantic deluge was submerging everything, even the infinite sky. Soon, there was nothing but a perpetual sea. The next moment, this sea was a titanic landmass, a fertile ground. From the void above, a seed fell into the soil.
What was a tiny seed suddenly became a world tree. It spread its branches and created a new sky beneath the void while its roots burrowed throughout the infinite land. The tree was Cao Yun while the soil was Feng Yingyue. Wood was slowly devouring Earth, though. Earth could feed Wood but it wouldn't last very long when their Essence Fire penetrated this new world. Fire rained down from the void and began to consume the branches of the world tree. Fire was being fueled by Wood and created ash that fell to the soil, in return nourishing Earth.
Wood, Fire and Earth were in a perpetual cycle. Without Fire, Wood would consume Earth. Without Earth, Fire would consume Wood. Without Wood, Earth would consume Fire. But as all three elements were balancing each other out, they were all benefiting. However, the balance was fragile and ever-changing. As such, both Cao Yun and Feng Yingyue had to adapt, they could not stay immobile or passive. Not only did they have to activate their bodies, but they also needed to merge their very souls now. Their souls were the cauldrons and they had to merge together into one singular cauldron so they could go on in the 'Twin Flesh Furnaces, Soul Cauldron' method.
Now that their bodies had become the perfect furnace and had given birth to a great Essence Fire, they needed a cauldron that was sturdy enough to resist it.
As its branches were being burned, the world tree began to change and adapt, its branches twisted and coiled around each other, trying to become thicker and thicker. Within Cao Yun's heart, his Solar-Orchid Flame was reacting, altering the properties of the tree. But, above all else, he could feel the seed of the world tree acting up. That seed's influence was all over his Nine Soul Peaks and then spread throughout his meridians and vessels. Soon, it spread within Feng Yingyue's body as well, strengthening her meridians and vessels just as she was about to make her two Dantian collide.
Slowly, the immense tree took on a different shape, as Cao Yun's seven Piercing Stars reacted in his own sea of consciousness. Indeed, the branches began to form the shape of a serpentine creature. A dragon as large as an entire galaxy was being born out of the branches. As it was still being attacked by the Essence Fire, the Wood dragon tried to dig deeper and deeper into the soil. But the soil wouldn't remain still, doing nothing. Large pillars of dirt shot up toward the branches, trying to reach the fire above in order to catch more of the ashes falling from the branches.
From the infinite ground, a large shape began to emerge as dirt was flying all over the place. It was a gigantic bird whose wings were large enough to cover all of the stars in the night sky. Those wings were trying to encase the dragon, but the dragon was slippery. For eons, the two mythical creatures chased one another. Unfortunately, they couldn't escape as they were both connected by the trunk of the world tree, growing stronger and stronger.
The Essence Fire was growing increasingly more violent as the two beasts were dancing against one another, alternatively trying to catch the other or escape from it. The void was now only made of this Essence Fire.
At last, the two beasts stopped antagonizing each other. After more than an eternity, they embraced each other. Just as Cao Yun and Feng Yingyue were dancing, the two mythical beasts began to dance against one another. The Essence Fire spread throughout their bodies, through the branches of the Wood dragon and into the dirt of the Earth bird. Soon, it was impossible to see any distinction between the two. At the very center, the majestic trunk remained but everything else was bathed in the Essence Fire as Wood and Earth were mixed together.
From Cao Yun's soul, bits and pieces were drawn into Feng Yingyue. And from her own soul, Cao Yun was also receiving images and thoughts, sensations and feelings. Their two souls were now perfectly melded. In other words, there was no secret between them, no hiding. If they had not been perfectly harmonized at that moment, this shock might have been enough to interrupt the dual cultivation. In fact, this was the step where most cultivators failed. Each one was afraid that their partner would see something they didn't want to share. And even when that wasn't the case, they might fear losing their own sense of self. For Cao Yun, this absolutely wasn't an issue.
The young man had understood many things about the self. What he thought was his self was in fact a perpetual interaction between many parts. He could never point at anything and claim that it was him, only that it was influencing him in some way. But this elusive self had disappeared as Cao Yun began to better understand that this sensation was mostly an illusion. The question itself had been rendered moot by his better understanding of souls and minds. Ironically, now that Cao Yun had lost his delusions about the self, his sense of self felt even stronger than before. Indeed, he had no fear of losing something that was never his, and in fact, never there to begin with.
As their souls merged, Cao Yun discovered that Feng Yingyue had had different experiences with her self and her soul. In fact, she had come to different conclusions as well. Instead of rejecting them, which would have caused a clash, Cao Yun accepted them completely. All new ideas and experiences were good for his comprehension. Feng Yingyue saw the self as an emanation of the Dao itself. It was being influenced by the souls and the five elements, as well as yin and yang, just like anything else within nature. But she did associate her self with a part of the Dao. For her, understanding the Dao was also understanding herself. Her body was just a medium used by the Dao to understand itself further by studying the nature that had emerged from itself.
Besides all these ideas and visions of the world, Cao Yun and Feng Yingyue also saw all the memories of their partner. Feng Yingyue saw the tragedy of Cao Yun, she felt his pain, but she also felt his achievements.
Her mind naturally went to Cao Yun's memories about his own Lesser Tribulation, as hers was literally happening at the moment. Then, her two crystallized Dantian began to move. At the same moment, Cao Yun could feel his own Soul Embryo moving around. It was like a small baby fidgeting. As Cao Yun's soul was fully immersed within Feng Yingyue's, it naturally began to seep into his Soul Embryo. Cao Yun was about to break through to the 6th-grade Spirit Warrior stage just as Feng Yingyue was about to become an 8th-grade Mortal Warrior.
As the two mythical beasts were dancing around each other, completely losing themselves into the other to the point where it was impossible to discern one from the other, Cao Yun and Feng Yingyue lost themselves in their breakthroughs. It was as if both of them were living the other's breakthrough as well. And, in a sense, it was the case.
Suddenly, Feng Yingyue's crystallized Dantian collided. They rushed toward Feng Yingyue's Huang Ting, the Yellow Court. As they entered this Yellow Court, they exploded against each other. A gigantic explosion shook Feng Yingyue's body. All of her muscles contracted and she began to convulse. Under such violence and bliss, she lost herself in Cao Yun's kiss. Both lovers were literally floating above the bed as Cao Yun's spiritual senses were all over the place. Their embrace was so tight that they were leaving marks on the other's flesh. Of course, Cao Yun's strength was under control or he might have actually crushed his partner to death.
A torrent of violent energy spread from Feng Yingyue's Yellow Court as her two Dantian had collided. From Cao Yun's body, wild energies were pressing against Feng Yingyue. As a result, they were containing this violent explosion within her Yellow Court. It had nowhere to go. In that moment, both her crystallized Dantian had been pulverized. And yet, the violent explosion could not escape. As such, it kept breaking apart her crystallized Dantian, making her breakthrough more and more thorough. However, there was a real risk that it would damage her body. At some point, the pressure had to be released and it would go through her flesh and meridians. As such, she might not be able to survive it.
That being said, the world tree seed within Cao Yun spread its influence. With it, the Drop of Wrath also spread its influence, and so did the Solar-Orchid Flame. They all reached Feng Yingyue's Yellow Court. In order for Feng Yingyue to produce the best possible Soul Embryo, her two crystallized Dantian had to be thoroughly destroyed. Right now, they were so atomized that this exceeded even what Cao Yun had gone through. But it was reaching its absolute limit.
Instinctively, she felt the need to release all this energy. And so did Cao Yun. It was time to enter the last stages of 'Twin Flesh Furnaces, Soul Cauldron'.