Back then, to complete Hong'er, Ni Xuan created an artifact soul, a sword soul, and fused it with Hong'er. After the fusion, Hong'er became a being that was half-sword, half-human, with the soul of both a person and a sword.
The most ideal way to help You'er become whole and leave this place to explore the outside world would be to create an artifact soul and fuse it with her soul. However, the problem is that creating a second artifact soul, like the one Ni Xuan made, is impossible.
Ni Xuan needed at least thousands of Celestial Spirit Divine Swords at the minimum before he could start creating Hong'er's divine soul. He also paid a huge price during the fusion process.
Even in the prosperous era of the old Primal Chaos, such a feat was nearly impossible to replicate. If it were possible, Ni Xuan would have surely created a sword soul for You'er as well. However, today, it is impossible to find even a single sword that is of divine quality, making it impossible to create a sword soul for You'er.
Thus, the only viable solution is for You'er to share Hong'er's sword soul.
They were originally one being, so the likelihood of conflict or rejection between them is almost nonexistent. Another crucial factor is Yun Wuji, he's the only one, aside from the (technically) deceased Ancestral Goddess, who completely disregards the fundamental laws of light and darkness.
Hong'er's main attribute is Light, while You'er's attribute is Darkness. No one else could even consider attempting this fusion because light and darkness are inherently incompatible. If anyone other than Yun Wuji tried, they would almost certainly meet a horrific end.
What gives Yun Wuji confidence in his success is the fact that, in the novel, they had successfully shared the soul sword together. As long as he follows the correct process, he believes nothing unexpected will happen.
A red light shot out from the vermilion sword mark, responding to Yun Wuji's mental summons, and Hong'er appeared right before him. The girl let out a lazy yawn and then asked, "You want me to share my sword soul with You'er? Does this mean she'll be 'moving in' with me in my sword soul?"
Yun Wuji had visited this place many times with his main body over the past two years, so Hong'er had met You'er and they had spent a lot of time together, playing and getting to know each other.
"..." Mu Bingyun's eyes widened slightly, standing silently as she observed the two girls. This was her first time witnessing such entities. However, because of her calm and composed nature, she chose not to interrupt Yun Wuji at this moment.
She could always ask him later.
"Yes."
Before coming here, Yun Wuji had already spoken to Hong'er, and as expected, convincing her was effortless. The moment he told her the news, the little girl jumped with joy. She was extremely happy to have You'er with her.
Yun Wuji lowered his body slightly, asking once more to confirm, "So... are you sure you're okay with this?"
"Of course I'm okay with this!" Hong'er's eyes curved into crescents. "I really like You'er! Does this mean I can play with her all the time?"
"Yes, you and You'er will be together forever from now on," Yun Wuji patted her head with a smile, nodding in affirmation.
"That's great, then! I want to be with You'er forever!" Hong'er grinned as she looked at You'er, her eyes filled with excitement.
"Good," Yun Wuji smiled back. Then, with a gentle nod, he told her, "Hong'er, turn into a sword."
Hong'er obeyed, and with a flash of vermilion light emanating from both of them, she transformed into the Heaven Smiting Devil Slayer Sword.
Yun Wuji grasped the heavy sword and approached You'er. He smiled and said, "I'm going to start. Whatever happens from now on, you must not resist, alright?"
"…" You'er gazed at him with her quad-colored eyes, brimming with anticipation, and nodded quickly.
Yun Wuji extended his hand above her head, and a dark profound formation materialized. The shadowy formation began to spin rapidly over her.
Next, a formation bigger than the first appeared in front of him, spinning as well. The speed and rhythm of rotation of both formations were exactly the same, as if they were linked by something.
"Dark Profound Energy!" Mu Bingyun froze, her mouth wide open in shock, and she staggered back a few steps, her eyes fixed on him.
As the two formations continued, Yun Wuji unleashed his life and soul aura completely. In this state, literally any power could invade his life energy or mental energy.
If anyone wanted to harm him right now, they would only need a sliver of their profound energy to invade his mind and body.
The only person present right now was Mu Bingyun, and Yun Wuji was absolutely certain she wouldn't do anything to harm him.
His act of completely dropping his guard in front of her, entrusting his life to her without hesitation, made Mu Bingyun's heart pound. Instinctively, she pressed both hands to her chest.
Dark light suddenly shot from the formation above You'er, streaking into the formation before Yun Wuji. The two formations now connected You'er and Yun Wuji's soul and life energy. Gradually, the formations began rotating in reverse, and as they did, You'er's body started glowing with silver light until it completely enveloped her.
In the next moment, the silver light entered the profound formation above her and was pulled into the larger formation in front of Yun Wuji, before finally entering his body.
Once it did, a soundless silver explosion erupted, illuminating the darkness like a shining beacon in this place of absolute blackness.
A few breaths later, the light faded, and Yun Wuji's body was revealed to Mu Bingyun's eyes. he was completely the same, as if nothing had changed in him.
Standing quietly next to him was a heavy sword. It had the exact same blade as the Heaven Smiting Devil Slayer Sword with several differences. One, it was bright silver in color, just like You'er's silver hair.
Two, a black fog was circulating around its body.
And three, the gem connecting the hilt and the blade was now quad-colored instead of vermilion. They matched perfectly with You'er's pupils.
Inside the gem, a pocket-sized You'er could be seen swimming around in an unfamiliar world. She seemed to be extremely interested and confused by everything around her.
On both sides of the sword, a new name was engraved: Heaven Smiting Devil Emperor Sword.
Yun Wuji studied the newly transformed sword before him but didn't immediately reach for it. Instead, he looked inside the Sky Poison Pearl, where Hong'er lay curled up, eyes shut tight in deep sleep.
The two girls couldn't manifest as swords simultaneously. When one took blade form, the other would be forced into dormancy. This was because, despite his disregard for the contradiction between Light and Darkness, they couldn't.
Probably, the only way for them to unleash all their power was when they fused together.
He stretched out both hands and grabbed the hilt. Then, he put strength into his arms.
His arms and his face instantly turned distorted at the same time, and he almost stumbled on his own feet.
It was because the sword hadn't moved in the slightest.
"Fuck!!!" Yun Wuji roared with all his might, veins bulging from both his arms and neck, but... the giant sword glowing darkly on the ground still didn't move an inch.
Boom! Boom! Boom!
Refusing to give up, Yun Wuji's whole body tensed, as if he were straining every muscle. Successive bursts of profound energy erupted from his body one after another, causing wave after wave of fierce wind. The silver sword finally moved slowly under Yun Wuji's power, and he eventually managed to keep the tip pointed at the dark space in front of him.
Yun Wuji's arms and teeth were shaking. Excluding 'Invictus,' he was already using all his strength, but he was barely able to lift the Devil Emperor Sword. When he tried to perform a swing, his arms gave out just as he lifted the sword into position.
Bang!!
The Heaven Smiting Devil Emperor Sword fell heavily to the ground, causing a terrible earthquake that shook this world of darkness.
"Fuck, it's so heavy!" Yun Wuji was still holding onto the sword, unable to lift it anymore. He didn't feel depressed because he already knew this would happen, and even if he hadn't, he wouldn't feel sad either. The stronger and heavier the sword was, the better it was for him. Because once he grew strong enough, wielding this sword would unleash much greater power, rather than him outgrowing his weapon.
After all, with his insane rate of growth, it was just a matter of time before all weapons in the Primal Chaos (excluding heavenly treasures) would become useless to him. So, the stronger the Heaven Smiting Devil Emperor Sword was, the happier Yun Wuji was.
"You'er," he let go of the sword and called out softly.
There was a silvery black flash, and the Heaven Smiting Devil Emperor Sword instantly transformed back into You'er. It was immediately followed by a red flash as Hong'er jumped out on her own and blinked her eyes rapidly, asking, "Eh? Why did I suddenly fall asleep just now? Did you do something weird to me just now, Big Brother?"
"-_-|||" Yun Wuji's face darkened, and he resisted the urge to smack her head.
"Eh?" She suddenly turned around and looked at You'er next to her. You'er was staring at her as well. The duo looked into each other's eyes for a long time, almost as if they were frozen... until finally, they extended a hand at the same time and touched each other's cheeks.
This time, their hands didn't pass through each other's body... Hong'er felt something icy at the tip of her fingers, and You'er felt a surge of warmth that was both unfamiliar and unspeakably strange.
"Wah!" Hong'er's eyes lit up like the stars. "I can finally touch You'er... Wah!"
Hong'er cheered happily. She didn't know why she was so happy, nor did she want to. She didn't realize it, but a pair of tears were flowing down her cheeks even though she was laughing in joy.
You'er slowly withdrew her hand before staring blankly at her palm for some time. Then, she very, very carefully touched Yun Wuji's palm with a finger and felt a different kind of warmth.
This time, she didn't withdraw her hand. Instead, she stared into Yun Wuji's eyes and tried very hard to narrow her eyes and curl her lips, displaying... a near-perfect smile for everyone to see.
Yun Wuji felt the corner of his eyes becoming wet. He turned around and wiped his eyes, It was like seeing his ill daughter finally recovering; her smile pierced the softest part of his heart!
He squatted down and spread his arms, holding the two girls in his embrace. He said with a gentle smile, "Hong'er, You'er, you two must be quite tired after the fusion. Why don't you go enjoy a nice nap, okay? I'll show you the outside world after you've awakened, You'er."
You'er nodded and opened her mouth slightly. "Mn..."
...
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