This song is a pure piece of music composed by Chen Xunqi.
"The Solitary Shadow on Heaven and Earth Let Me Go" was quoted in the movie "Westward Journey" because of its extremely desolate and majestic music style, which is both heroic and tragic.
At the end of Westward Journey, Zixia said to Zhizunbao when she died: I guessed the beginning, but I couldn’t guess the ending. The background music at this time is "The Solitary Shadow of Heaven and Earth Let Me Go".
Extended information
"The Shadow of the World" was first adapted from Wong Kar-Wai's classic film "Ashes of Time" and was composed by Hong Kong film genius Chen Xunqi. This music is used at the beginning and end of "Ashes of Time" and is also the background music when Zixia dies in "Journey to the West".
In "Unparalleled", Tony Leung rode his horse to rob the princess of her wedding and raised peach blossom petals all over the ground. It was also this song.
This is also the background music used when Han Dieer goes to investigate the corpse of Wolong in "The Master of Heavenly Master Zhongkui Singapore Version".
This is also the song used in Lu Songxian's version of "The Swordsman" when Fei Bin was killed by Mo Da, when Linghu Chong buried Ning Zhongze, and when Yue Buqun was killed by Yilin at Siguo Cliff in Mount Huashan.
This piece of music was also used many times in Huang Rihua's version of "The Eight Parts of the Dragon".
Reference material: Baidu Encyclopedia entry—The solitary shadow of heaven and earth is left to my own devices