These two mirrors (青銅鏡, lit. "bronze mirrors") play an important part in Shenmue and are introduced to us right at the beginning of the first game. When LanDi came to the Hazuki Dojo he demanded "the mirror" in exchange for Ryo's life. It's interesting to note that LanDi only asked for one mirror, and didn't specify the design indicating that he either doesn't know Iwao had both mirrors, or isn't even aware there are two designs. LanDi left in possession of the Dragon Mirror (龍鏡) which Iwao had buried underneath a cherry tree beside the Dojo.
The second mirror, the Phoenix Mirror (鳳凰鏡), Ryo learns of from Master Chen and he later finds it hidden in a box in a hollowed out section of the secret basement of the Hazuki Dojo. Ryo also learns from Master Chen that the mirrors are made from a precious stone called Phantom River Stone and that Yuanda Zhu once told him that if "the Dragon and Phoenix meet, the gates of Heaven and Earth will open and Chiyou will resurrect itself on Earth". Whilst Master Chen is unsure of exactly what LanDi is planning to do with both mirrors, he tells Ryo he must not allow him to get hold of the Phoenix Mirror as well.
It's not until Ryo gets to finally meet with Yuandha Zhu in Kowloon that he learns anymore about the two Mirrors. The two mirrors belonged to Sunming Zhao and Iwao brought them back to Japan. He goes on to explain that when the two mirrors are brought together they form a key to treasures "hidden away in order to revive the Qing Dynasty". Using the light of a candle and smoke blown over the mirror lights appear above the mirror to form the constellation "The Big Dipper". This forms part of a map, but only one mirror is not enough, the light of the Dragon Mirror is also needed to see the full map. We also learn from Yuandha Zhu that Phantom River Stone can only be found in one place, Bailu Village in Guilin, and the descendants of whoever made the mirrors should still live in the village.
Next in Guilin, Ryo finds a diagram for both the Dragon and Phoenix mirrors in Shenhua's house. Shenhua explains that all she knows about it is that her step-father has said it had been in his family for a long time. This probably indicates that Shenhua's step-father is a descendant of someone who had a hand in making the Dragon and Phoenix Mirror, but we don't know this for certain. The next day Shenhua and Ryo go to the Stone Pit where her step-father is said to be gathering Phantom River Stone but he isn't there. However they do find a giant version of the both the Dragon and Phoenix Mirror carved into the wall of the pit.. and that is all we know.