The vow to reincarnate came from a series of fantasy novels," Douluo Continent," and its derivative works, written by the Chinese online writer Tang Sanshao. The content was: " I am willing." "I'm willing." "If there is a next life, we will never meet again."
"Douluo Continent" told the story of how Tang San, who had transmigrated to the Douluo Continent, cultivated his spirit step by step, becoming a god from a human, and finally eradicated the evil forces on the Douluo Continent, avenging his mother's death, becoming the Douluo Continent's strongest person. In the novel, reincarnation was a special form of love. In this form of love, if one of the lovers died, the other party could use his soul as the price to revive the dead person in another form, but the revived person would lose the memories of the previous life.
While waiting for the TV series, you can also click on the link below to read the original work of " Little Fox Demon Matchmaker " to understand the plot in advance!
Another possibility for 'The Vow' is that it's a fictional story in a book or a movie. It could involve characters who are bound by a vow, perhaps a vow of revenge. The story might unfold as they strive to fulfill this vow, facing various obstacles and moral dilemmas along the way. Their relationships with other characters would be affected by this vow, and the plot could revolve around the consequences of their actions in relation to the vow.
It is indeed a true story. The show takes inspiration from actual happenings and presents them in a dramatized form. However, some elements might be embellished for entertainment value while still maintaining the core truth.