One year after the second defeat of the Spirit of Dark Power, My Melody and her friends returned to Mariland until Baku "dropped a bomb" in the middle of the flower field, taking out black notes all over Mari Land and the human world. After a short while, Mariland had their "high court" and took the king off the throne. When the time came to choose the next ruler, a black note came to the minister, turning him into a "Huff-Huff" which is a residue of Dar-chan. My Melody refreshed him and was chosen to be a candidate for princess. However, she has to pass a trial by turning all of the black notes into Twinkle Gems to put in her crown. As soon as Kuromi heard this, she was outraged as she wanted to become the princess as well, but then a very mysterious woman came with an intriguing offer. Kuromi now has to collect Anger Gems and put them in her crown to become the Dark Princess and rule over Mari Land. The two decide to go to the human world and collect every black note for them to become the next ruler of Mari Land. Unbeknownst to everyone, the spirit again will make its rise as he intends to plunge both Earth and Mariland into eternal darkness.

(Source: Wikipedia)