Dark Qilin Bone was the bone of a quasi-divine-beast. It could be considered as a sacred grade immortal ingredient, but it was of the lowest quality. Nevertheless, it was still a good ingredient. Besides, the bone was where all the Qilin's essence was stored, so it contained endless spirit essence and divine energy, making it the best ingredient to make soup. During cooking, the energy in the bone would seep out and fuse with the soup, and could be completely absorbed by the human body.
It was the reason why Bu Fang wanted to cook this dish. The curse in Nethery's body needed to be suppressed by dishes rich in spirit essence, so a bowl tonic soup cooked with the Qilin bone was a perfect choice.