Ningguang is Guizhong’s rebirth or reincarnation. I'll mention some “coincidences” that tie Ninggunag to Guizhong.
Glaze Lilies: Glaze Lilies were in bloom when Zhongli first met Guizhong and during their final parting. Zhongli says true wild glaze lilies were found in Dihua Marsh and Guili Plains. Ningguang is also associated with glaze lilies because they are her ascension materials as well as the fact that she goes on about how lovely and expensive they are in a voice line as well, in fact she’s the one who tells us in that same voice line that Yujing Terrace is the place where they’re grown.
Memory of Dust: This weapon was a gift from Guizhong to Zhongli and is a puzzle he’s been unable to solve confirming the association to Guizhong again. Also Dust implies Guizhong, goddess of dust. It’s also one of the very few catalyst weapons in the game that mesh perfectly with Ningguang’s talent kit. In fact its passive talent is completely worthless on anyone but Ningguang as she’s the only catalyst user who creates shields.
Ideologies: Guizhong has been characteristically kind and deeply understanding of humans and human motives. At first glance Ningguang seems to be none of these things but her character stories show that she actually goes down and plays with children and values their opinions on the happenings of Liyue so much that she uses them as her “intelligence network.” She also simply enjoys their company, showing that she is not the cold hearted businesswoman people make her out to be.
Engineering: Guizhong happened to be one of the greatest engineers among gods and adepti, on the other hand Ningguang has built neumrous wonders of engineering such as jade chamber, she also made a modified version of guizhong ballista to fight the wife of Osial.
Ningguang didn't receive any vision she was going to sell a masterless vision when it got awakened by her presence.
Ningguang is also associated with the Phoenix in her namecard and leg tattoo. This could mean with the common western theme of phoenixes is that she was reborn which entirely fits this theory.
In Zhongli’s leaked voice lines he refers to Ningguang in an incredibly fond and somber tone calling her a “rare gem”.
Artwork by @dandeeca2 on twitter.
Main theory by valainistima on reddit.
