Promise
The first promise Persephone made was to the mortals. At first under her mother's guidance, and then on her own, she gave to them the gift of spring and its promise of life, and vowed to return to them every year. She brought flowers, hand-picked from her garden, on every visit, and as the centuries passed she grew more beautiful, outspoken, and bold.
The second promise she made was to her mother—that she would only marry for love, and not any political gain. Who would have thought that Hades himself would light the fire in her heart? Becoming Queen of the Underworld was a bonus compared to Hades' love, and Persephone wore her crown with pride.
The third promise she made was to Hades himself. She had to go back; the world was cold and dying without her. If Persephone never stepped foot aboveground, the flowers would never bloom, fruit would never grow, and spring would never come. But she promised that when enough time had passed, she would return to the Underworld as its queen, as his wife.
Hades dearly wished he could believe that promise.