Centuries ago, the land of China was full of magical spirits. Those who could utilize the power of spirits were called Exorcists. Their duty was to prevent the Great Diablo, a demon that shows up once every millennium, from plaguing the world. In the Han Dynasty, however, in a catastrophe known as The Oblivion, all magical spirits vanished overnight. Having lost their powers, Exorcists became a thing of the past.
Later, during the incessant war between the Qin and Jin Kingdoms, the resentful spirits of those who died in vain became the nutrients triggering the revival of the Great Diablo. In order to stop the demon, Chen Xing, the last surviving Exorcist, starts a journey with "Lamp of the Heart", a magical artifact that lives in his soul. He is to travel to Xiangyang City to find Xiangshu, who is destined to join him and defeat the demon.
(Source: Youtube Description, edited)
— Description from AniList community (anilist.co).
