Actually, Ruby's problem is quite obvious, which is... she has always been imitating Xingye Ai.
Duanmu Huai is well aware of this, after all, he's been an avid fan since he was a baby, and he's tired of it.
The answer is actually quite standard; you just need to tell her, "Don't imitate Xingye Ai, just be yourself."
But reality is not that easy. Humans, by nature, are the type that won't stop even when they know they're making a mistake.
Not everyone has the ability to correct themselves once they know they're wrong.
It's easy to say, but not that easy to truly change.
So, Duanmu Huai decided to give Ruby a strong dose.
He first found Hei Chuan Chi Yin — an expert in performing Ghost Possession. Ruby had been infatuated with Xingye Ai since birth, but when it comes to imitating Xingye Ai, she couldn't compete with Hei Chuan Chi Yin, who, after being commissioned by Duanmu Huai, spent two nights researching and embodying Xingye Ai.
