Tsukushi Makino:
Dijun after killing LHJ used his ribs to create XJ and sealed LHJ into that crystal Lamp that's why XJ doesn't have any memory of past bcoz there is no past. The pridominal soul of LHD in that crystal lamp has connection with XJ as she is made from his ribs and what's the best way to connect something is DNA - blood. I only remember this much
Making a woman out of ribs concept has been used in an earlier show "The Journey"
https://mydramalist.com/21024-the-journey
https://mydramalist.com/22610-the-journey-2
I have never watched the series at all, but from a glance reading the viewers on that site, even though Yeyin comes from the body part of Yalong, but Yeyin does not change back into the body of Yalong, besides that Yalong was not killed by Siyin at that time ..... !!! In fact, at the end of the story, Yeyin committed suicide ..... !!!
So, the case in the TV series is not the same as the one here .... Xuanji is basically just a transgender woman, because in Xuanji's body there is a body figure of an older man (Star of Mosha) .... !! ^^