These two hearts of the Black Dragon could obviously no longer be the original hearts of a Black Dragon. They were instead special magical tools fashioned out of the heart of a Black Dragon. According to Little Zi's research findings, these two hearts were originally intended for forming a powerful undead creature by using necromancy to assemble dead bodies. However, there were flaws in the design, causing the resultant creature to collapse again after a short while.
Therefore, Little Zi estimated, these two hearts were thrown into magma for destruction.
However, the Dragon Power contained in the heart of a Black Dragon was extremely powerful and it instinctively protected itself as it wandered through the magma. Ultimately, it found its way onto this mysterious island and, by some strange twist of fate, obtained the Giant's Weapon.
The Giant's Weapon contained almost infinite power, and the two hearts of the Black Dragon simply hid in the magma beneath the island.