"To think like a dragon obviously refers to a mind-nourishing method. The thing you imagine when you nourish your mind must be a physical object, hence the dragon here must exist physically."
"Nonsense! Are cool breeze and moonlight tangible? They were used for inward contemplation before. And what about the 'dominate all things in the world like a dragon'? Obviously it is talking about a state of mind; it's a metaphor."
"I don't think it's a metaphor. It should be something real."
"It must be a metaphor…"
"Knock knock knock!"
Inside the room, the two were engaging in a fierce argument, a stark contrast to the usual indifferent and peaceful atmosphere between them.
However, a knock came from the door suddenly, followed by Xiaojin's voice, "What's going on in there? You do realize you can always vent those passion on each other, right? Why use words when you can get physical? My ears are aching from all your talking!"
The two were all hyped up and she had to show up at this moment for some "sisterly love". Well, she had it coming.
Xiaozhai reached the door in a couple of strides and yanked it open. Squeaks and whines streamed in. "Sister, I'm sorry! I'm so sorry! Ah, that hurts, hurts! Forgive me… I'm on my way, right now…"
Then with a loud bang, the door was closed and all was quiet again.
The two also took a break, relaxing their minds in the meantime.
The paragraph from Tan Chongdai's secret records was probably something along the line of a general principle. Because it contained no specific cultivating method, the two of them had to deduce things little by little. If they were to take the words literally, the text was basically saying:
"Wood belongs to the East, fire the South, metal the West, and water the North; together with earth in the Center, they make up the Five Elements of heaven and earth. The thunder is accumulated from the Five Elements, hence the Five Thunders.
Thunders carry out the commands of heaven and earth with utmost authority, dominating over any living creature within three realms and nine levels of the universe. And, 'dominating' means 'to absorb' as much as 'to terrify'.
That is to say, once the thunder technique is unleashed, the practitioner could absorb power from the surroundings as well as make everything bow to his power. When one reaches perfection in the thunder technique, he will become immortal."
The above paragraphs were quite easy to comprehend. Five Thunders corresponded to the Five Elements and five internal organs, which had something in common with Gu Yu's classification in that both connected the internal Five Elements with the external ones. The difference was that while Gu Yu used it to temper the physical body and concentrate the spirit, the secret record used it to breed the thunder energy.
Xiaozhai's sect originated during early Tang Dynasty when the essence-consuming method had not yet declined. All sects and schools would draw lessons from the method, hence what the secret record suggested made sense.
Everything was understandable apart from the last sentence, namely the "think like a dragon, act as unrestrained as a dragon, and dominate all things in the world like a dragon…" part.
They had been racking their brains over it and still could not reach a consensus. Did the dragon refer to the divine being soaring above all heavens? Or was it a metaphoric expression of a certain state in the same way as "Dan-bearing" and "Yuan Ying" did?
Apart from that, they also made another discovery. They had come to realize that recorded in the text was a comprehensive system of the thunder technique, because the idea of "inward contemplation" was mentioned.
What was called "visualization" in Buddhism was "inward contemplation" to Taoist followers—it was a secret method to nourish and refine the spirit. The cultivation of the mind was extremely difficult. A complete set of inheritance usually came with corresponding spirit-nourishing methods.
The reason why Gu Yu's Method of Consuming Six Essences was incomplete was the lack of a spirit-nourishing method.
On a whole, the information they acquired was so limited that these were the only things they could come up with.
In the following days, they visited the temple daily to exchange ideas and discuss theories with Tan Chongdai. The content of their discussion was substantial this time. Since the old priest counted on them to find a pupil to succeed his legacy, he was no longer hiding anything from them and explained in details about skills, talismans, and incantation.
Call it returning a favor or compensation, the fact was that Gu Yu helped Tan with dredging the stagnated Qi and blood in his body, while Xiaozhai even came up with a few body-tempering moves and left it to the old priest.
With these two approaches, other things aside, the life expectancy of the old priest was extended for another three years at least.
They arrived in the little courtyard rather bossy, even assuming an arrogant air sometimes. Yet as the events unfolded, it was quite hard to tell now which of the two sides was the debtor and which the creditor.
Before they knew it, the two had stayed in Jiang Zhou for over a week. They hardly went out for any sightseeing, but were completely occupied by the lousy business of Qionglong Mountain. Xiaojin would come over whenever she did not have classes and sleep over in her sister's room.
After a couple of days, she became quite close with Gu Yu, for while the big sister "terrified" her all the time, the brother-in-law doted on her.
The little rogue was seldom disciplined—if at all—during her childhood and left home for school when she hit puberty. Rebellious and ostentatious behavior was unavoidable. However, she could tell who were the people that genuinely cared for her.
That is to say, Gu Yu and Xiaozhai held a very special place in her heart. She could not help but feel attached to them.
Overcast, cold rain.
In the waiting hall of Jiang Zhou Railway Station, Xiaojin looked grumpy, for those two were leaving. To make it worse, they showed no sadness at parting whatsoever, but were deep in conversation in a low voice again.
According to their itinerary, they were heading for Tianzhu Mountain in Qian Zhou to examine the condition of spiritual essence there. After that, they would turn southwest and go straight to Shu Zhou.
Qian Zhou was not far, only a four-hour ride by train. Not many people were waiting for the train either. After whispering to each other for a while, they finally noticed the low-spirited younger sister.
"What's all that about? It's not like we'll never see each other again."
Seeing that Xiaojin pursed her lips with watery eyes, Xiaozhai could not help but tease her. "Don't tell me you are going to cry later."
She was a sentimental kid, but would never admit it herself. "I can't wait to see you guys off. It's been a week since I last had fun."
"Hehe, come to Bai Town for your winter vacation. I'll show you a good time," Gu Yu chimed in with a smile.
"It'll be ages before the winter vacation…"
Eyeing him, Xiaojin suddenly grabbed his arm and dragged him to the side. She whispered, "This alliance between us has not achieved anything yet. But don't give up. You have to work this thing out; think of it as a life-and-death struggle. You're leaving and I have nothing for you to take away but this little intangible 'cultural heritage'. Take it as a parting gift."
With that, she fumbled out a black pen and wrote something down on his palm.
"What is it?" He was confused.
"Never mind what it is. Just memorize it. It'll come handy some day!" She gave him a solemn promise.
The three chatted for a while more when the announcement suddenly sang out, "Dear passengers, Train No. DXXX from Jiang Zhou to Qian Zhou is now ready for ticket-checking…"
"Ok, that's our train," Xiaozhai lifted her backpack off the ground.
"You should go back. Drive carefully," said Gu Yu.
"Em, bye bye!"
The kid stood there and did not leave until they passed the checkpoint and walked onto the platform.
They boarded the train and found their seats. The carriage was not fully loaded—about a third of the seats was empty. Xiaozhai leaned against the window, texting someone on her phone.
Having nothing better to do, Gu Yu looked at his palm again. On it, Xiaojin had written "75d, 64, 38".
He could not see any pattern in this combination and had no idea what Xiaojin was getting at.
"What are you looking at?"
Xiaojin had finished texting and asked casually.
He flipped his hand to conceal his palm, but she still managed to steal a glimpse. The girl then said, "Well, those are the sizes of my bra, my waist and my shoes."
Gu Yu choked on his spit. 'Sis, do you mind not giving away such information with a nonchalant face?"
Right now, all he could think of was to rush back and give that young butt a good kick. He was then overwhelmed by embarrassment, self-conscious with the position of that hand, which ended up hanging awkwardly over his leg.
Xiaozhai seemed to notice none of this. She asked suddenly, "Hey, what was the bra size of your ex-girlfriend?"
"I, I'm not sure."
"Haven't you bought underwear for her before?"
"No, I haven't."
"Did she have nice breasts?"
"Stop! Stop right there!"
He wholeheartedly did not want to continue this subject. Wrying his face, he asked, "Can you ask something else?"
Xiaozhai paused and asked again: "Which do you prefer eating, bamboo shoots or steamed buns?" 
Gu Yu, "..."
ED/N: Thunder doesn't have a plural form in English, but we had to take some liberty with that because the translation would lose part of its meaning otherwise.
 TL/N: The "bamboo shoots" and "steamed buns" are "inappropriate" puns referring to the shape of female breasts.