When Min Ren became an Immortal Emperor his master, Dark Crow, chose one of the 12 Forbidden Burial Grounds for Min Ren's first battle. To any Immortal Emperor, the first battle was very important; it was an opportunity to refine the Heaven's Will. Min Ren personally led an army and successfully penetrated into the deepest depths of the Burial Ground.
One of the spoils of this battle was the Yin Yang Sea of Blood. Even Dark Crow was impressed with it and had hoped that Min Ren would use it to craft an Immortal Emperor Longevity Treasure that belonged to just him.
However, Min Ren already had a frighteningly powerful Longevity Treasure, so he was not willing to waste this treasure. In the end, he rewarded the Yin Yang Sea of Blood to Nine Saint Virtuous Paragon who exerted the most effort in this battle, as a praise.
However, Nine Saint Virtuous Paragon also hadn't used the Yin Yang Sea of Blood. Instead he sealed the Yin Yang Sea of Blood in the Nine Saint Demon Gate's Saint Cavern. Later on Nine Saint Virtuous Paragon asked Dark Crow to take care of the Nine Saint Demon Gate in the future and promised that he had left an indescribable treasure within the Gate as a payment.
Millions of years later, when Li Qiye opened the Saint Cavern, he finally understood that the treasure, promised to him by Nine Saint Virtuous Paragon, was the Yin Yang Sea of Blood. He took it away and left the Saint Cavern.
Several months later, when Li Qiye reached the Physique Accumulation level, he used the Revolving Crescent Sun Merit Law, Kun Peng's Six Variants and Hell Suppressing Deity Physique to subdue the Yin Yang Sea of Blood and refine it into his Longevity Treasure.
The Yin Yang Sea of Blood initially had a form of two drops of blood pearl, seemingly ordinary. They were formed by the condensation of two drops of fresh blood. However, with meticulous observation, one would find that the two blood pearls seemingly hid an endless amount of Blood Energy; it was as if they were two huge seas of blood. Plus, these two blood pearls were different, one blood pearl seemingly had a circular Golden Sun, slowly ascending, while the other blood pearl was akin to a circular Mysterious Moon, floating up and down without break.