After reaching the initial stage of the Huangji Realm, the "Qi Pool" had expanded dozens of times and was now approximately the size of a basketball.
However, the true energy within the Qi Pool was still extremely scarce, amounting to only the size of an egg and less than one-tenth of the pool's capacity.
Only by filling the Qi Pool with true energy could he advance to the middle stage of the Huangji Realm.
Zhang Ruochen sat cross-legged, closed his eyes, and activated the Shenwu Mark in his eyebrows. He then began to practice the first layer of the "Nine Heavens Mingdi Sutra", namely "Taihuang Huangjing Tian".
True energy flowed out of the Qi Pool and circulated through the meridians he had opened.
As the true energy coursed through his body, Zhang Ruochen's body seemed to transform into a vortex, gradually absorbing the spiritual energy between heaven and earth.
The spiritual energy between heaven and earth flowed into the Shenwu Mark in his eyebrows.
The Shenwu Mark then transformed this spiritual energy into true energy and stored it in the Qi Pool. The true energy then flowed out of the Qi Pool and circulated through the meridians.
After one complete cycle of the true energy in his body, it was considered one revolution.
After running nine revolutions, when Zhang Ruochen opened his eyes again, he discovered that the amount of true energy in his body had doubled, reaching one-tenth of the Qi Pool's capacity.
If other martial artists had known that they could double the amount of true energy in their bodies within such a short period of time, they would have been ecstatic.
However, Zhang Ruochen was still not satisfied and thought to himself, "After running nine revolutions, only a minimal increase in true energy has occurred. It's too slow! If only I could obtain a spirit crystal! That would significantly accelerate my cultivation speed!"
It should be noted that Zhang Ruochen was practicing the "Nine Heavens Mingdi Sutra", and his ability to absorb true energy was originally more rapid than that of martial artists who practiced lower-level skills.
The current cultivation speed naturally left him highly dissatisfied.
If he could obtain a spirit crystal, his cultivation speed could be greatly enhanced.
Spirit crystals are formed by the accumulation of spiritual energy.
They can be mined from underground ore veins as "natural spirit crystals" or obtained by killing monsters and extracting the "acquired spirit crystals" from their bodies.
The value of one spirit crystal is generally equivalent to that of one thousand silver coins. Only members of the royal family or talented individuals cultivated by large families have the opportunity to obtain spirit crystals.
One thousand silver coins is an astronomical sum for Zhang Ruochen and Lin Fei at present, and they simply cannot afford it.
"Spirit crystal!"
Zhang Ruochen's heart skipped a beat, and he immediately took out the white jujube-shaped crystal that he had always worn on his body and held it in the palm of his hand.
Could this be a spirit crystal?
As the true energy circulated within his body, the Shenwu Mark in his eyebrows immediately emerged and transformed into a circular halo about the size of a coin.
A white stream of true energy shot out from his eyebrows and struck the white crystal.
"Whoa!"
The surface of the white crystal was covered with four ancient characters.
This was extremely strange!
Zhang Ruochen had never seen such characters before, but he recognized them at a glance - "Space and Time Crystal".
It should be noted that in his previous life, Zhang Ruochen had also injected true energy into the white crystal, but he had never been able to activate the characters on the surface of the crystal.
"In my previous life, my cultivation level was hundreds of times stronger than it is now, and yet I still couldn't make the characters on the surface of the white crystal appear. Now, at the initial stage of the Huangji Realm, the white crystal has undergone a change. This clearly indicates that it's not due to the strength of the true energy but rather the attribute of the true energy."
For instance, martial artists with the Flaming Shenwu Mark achieve the best results when using fire-attributed spirit crystals, and their cultivation speed can be tripled. When using ordinary spirit crystals, the cultivation speed can only be doubled.
Ninety percent of the spirit crystals in nature have no attributes. Just like ninety percent of the martial artists can only activate martial arts marks without attributes.
"Could it be that my opened Shenwu Mark also possesses certain attributes and just happens to match this Space and Time Crystal? Wait a minute. What exactly is the Space and Time Crystal?"
Zhang Ruochen was well-informed in his previous life as the son of Emperor Ming and had heard of many types of attribute spirit crystals, such as the Flaming Spirit Crystal, the Mysterious Ice Spirit Crystal, the Thunder Spirit Crystal, and the Evil Blood Spirit Crystal... However, he had never heard of the Space and Time Attribute Spirit Crystal.
Because time and space are not things that humans can control. Even gods cannot influence time and space and must abide by the rules of time and space.
Just as Zhang Ruochen was still deeply puzzled, the surface of the Space and Time Crystal emitted a halo and transformed into a vortex.
The vortex continued to expand and enveloped Zhang Ruochen's body.
Zhang Ruochen only felt dizzy for a moment, and the next moment, he was transported to a closed space and landed heavily on the hard ground.
Fortunately, he had completed the Xisui and Chongmai process and reached the initial stage of the Huangji Realm, so his body had become stronger. If it were his weak body in the past, he would have died after falling down.
Zhang Ruochen got up from the ground, stretched his sore muscles and bones, and began to observe the space around him.
This space was completely sealed off, and there were no doors or windows. The height of the space was approximately ten meters, and the length and width were also approximately ten meters.
"How could this have happened? From where did I come? And where is this place? Eh! There is a stone platform over there!"
There was only one stone platform in the entire space.
On the stone platform was a rolled-up painting and a silver iron book. Other than that, there was nothing else!
Zhang Ruochen first went to pick up the painting, but the painting was extremely heavy, as if it were integrated with the stone platform. No matter how hard Zhang Ruochen tried, the painting didn't move at all.
Since he couldn't lift the painting or open it, Zhang Ruochen had to give up for the time being and then focused his attention on the thin silver iron book.
The surface of the silver iron book was inscribed with four characters: "The Secret Book of Space and Time!"
This time, Zhang Ruochen was prepared and used all his true energy to mobilize his entire strength to open the first page of the "Secret Book of Space and Time".
"It's so... effortless?"
It was extremely easy to turn the pages of the "Secret Book of Space and Time", and there was no effort involved at all.
Zhang Ruochen couldn't help shaking his head and stopped mobilizing the true energy. He picked up the "Secret Book of Space and Time" and held it in his hand, carefully reading it.
The first page of the "Secret Book of Space and Time" did not record any cultivation secrets but rather the notes of Sumeru Shengzang, the previous owner of the Space and Time Crystal.
After Zhang Ruochen finished reading Sumeru Shengzang's notes, he finally understood everything.
"Originally, the Shenwu Mark I opened is the Space and Time Shenwu Mark. According to Sumeru Shengzang, only one in a hundred million people can open the Space and Time Shenwu Mark. From ancient times to the present, there are only two people, plus me, making a total of three."
"Sumeru Shengzang is the second person to open the Space and Time Shenwu Mark. However, according to the records in the 'Secret Book of Space and Time' by him, he died more than one hundred thousand years ago. More than one hundred thousand years ago was already the Middle Ancient Era, which is far too distant from now."
The space Zhang Ruochen was in now was the inner space of the Space and Time Crystal.
The time flow speed in the inner space was completely different from that outside. It took three days to practice in the inner space, while only one day passed outside.
Zhang Ruochen was overjoyed and excitedly said, "Practicing for three days inside is equivalent to one day outside. This is simply three times more cultivation time than others! This is simply wonderful."
Zhang Ruochen wanted to turn to the second page of the "Secret Book of Space and Time", but no matter what he did, he couldn't open the second page.
"I can't open it again."
Zhang Ruochen had an urge to throw the "Secret Book of Space and Time" on the ground. Suddenly, he noticed a small line of words at the end of the first page.
"After reaching the small extreme position of the Huangji Realm, inject true energy into the painting scroll, and you can open the painting scroll."
Zhang Ruochen looked at the painting scroll again and guessed in his heart that there must be some mysterious skills recorded in the painting scroll, which might be related to the cultivation of time and space.
"I must work hard on my cultivation and strive to break through to the small extreme position as soon不已."
The "small extreme position" is the fourth small realm of the Huangji Realm, and above it are the middle extreme position, the big extreme position, and the great perfection.
Zhang Ruochen's abdomen felt hungry, so he immediately returned to his room from the inner space of the Space and Time Crystal.
He held the Space and Time Crystal tightly in his hand. With this crystal, he had a greater chance of reaching the middle stage of the Huangji Realm within three months.
Zhang Ruochen, Lin Fei, and the maid Yun'er sat together to have breakfast.
What they ate was only white rice and steamed buns, and there was no meat at all.
For martial artists, the physical strength they consumed was much greater than that of ordinary people, so the food they ate was of great significance.
Other princes and princesses who had opened the Shenwu Mark ate "Blood Dan" made from the blood of monsters every day and no longer consumed ordinary food.
After taking a Blood Dan, they could replenish the physical strength consumed throughout the day, and they would not feel hungry even if they practiced martial arts for a day.
Moreover, taking Blood Dan could also improve blood qi, strengthen the martial body, and increase physical strength.
If Zhang Ruochen only ate white rice and steamed buns, even if he ate eight meals a day, it would not be sufficient to meet the needs of his body.
"Chen'er, now that you have opened the Shenwu Mark, you can't eat ordinary food anymore. Take these ten Blood Dans first. If it's not enough, mother will think of other ways." Lin Fei took out a jade bottle and handed it to Zhang Ruochen.
Zhang Ruochen was still chewing on a steamed bun and was completely astonished when he heard that Lin Fei could take out ten Blood Dans. He asked with some confusion, "Mother, it costs five silver coins to buy one Blood Dan, and ten Blood Dans amount to fifty silver coins. Where did you get so much money?"
Lin Fei smiled and said, "Mother always has her ways."
The maid Yun'er stood behind Lin Fei and said, "Your Majesty sold her favorite hairpin to exchange for ten Blood Dans at the Dan Market!"
Lin Fei gently glared at Yun'er, as if blaming her for talking too much. Then she said, "Chen'er, don't think too much. As long as you can cultivate into a real martial artist, mother will support your cultivation no matter how many ornaments she sells."
Zhang Ruochen was deeply touched in his heart. He tightly held the jade bottle in his hand and bit his lip, really wanting to tell Lin Fei that he had already become a real martial artist.
No, he couldn't do that.
It was too fast to open the Qi Pool and complete the Xisui and Chongmai process in one night. If the news were to leak out accidentally, it would definitely reach the ears of other princes and the queen. At that time, it would not only harm himself but also harm Lin Fei.
He was still too weak at present and needed to acquire more powerful strength.