Chapter 224 - 223: Fusion
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.