This is a classic Chinese fairy tale. It tells of a poisonous grass that kills those who eat it, turning them into ghosts. These ghosts can only reincarnate by finding another victim of the same grass.
A young man named Zhu Sheng was traveling on a hot summer day. Feeling thirsty, he stopped at a roadside teahouse run by a woman named Ms. Kou and eagerly drank the tea she served. Upon returning home, he felt a sharp stomach pain and realized Ms. Kou had poisoned his tea to secure her own reincarnation. Filled with hatred, Zhu Sheng vowed revenge.
After his death, Zhu Sheng took Ms. Kou to the nether world, where they married. Back in the human world, Zhu Sheng's mother grieved deeply for her lost son. Hearing her cries, Zhu Sheng persuaded his wife to return with him to care for his mother. The ghostly couple worked hard to comfort and support the old woman.
Though their life improved, the mother remained uneasy knowing her son and daughter-in-law were ghosts. She pleaded with them to find replacements to move on. However, Zhu Sheng refused, saying, "I will not act against divine will and reason. My only wish is to care for you and ensure your happiness."
The couple devoted themselves to the mother until her natural death. Touched by their filial piety and righteousness, the gods sent a fairy cart to bring them to heaven, where they attained immortality.