Akumu serves as the main antagonist of Mewkledreamy Mix!. Her original name was Omoro, and approximately two thousand years ago, she was the queen of the Miracle Dreamy Kingdom. During that time, she loved interesting things and desired to build Amusing Land to make everyone feel excited, which led her to begin collecting people's dreams. Eventually, normal dreams could no longer satisfy her, so she decided to spread nightmares and changed her name to Akumu, a word that means nightmare in Japanese. Her goal became to transform hopes and dreams into nightmares and to build Nightmare Land. Her actions once caused the world to be covered in nightmares, but she was eventually sealed away at Ichigo Hill. She remained trapped there until the end of the first season, when the collapse of Lyra's Nightmare Castle at the hill released her.

Akumu has a personality defined by her love for interesting things and her wish to change positive dreams into terrifying ones. As the story of Mewkledreamy Mix! progresses, she takes on the role of the new boss for Yuni, Tsugi, and Hagi. She also approaches Akihito Sugiyama, believing he is excellent, and asks for his help to spread nightmares. To aid Akihito, who is not performing at his normal level due to his feelings for Yume, Akumu also reaches out to Haruhito Sugiyama and Ritsu Imai to convince them to join her side. Her development traces a clear path from a queen who sought excitement and amusement to a figure consumed by the desire for nightmares, having abandoned her original identity as Omoro to build Nightmare Land. While her specific supernatural or dream-based abilities are not detailed in available sources, her power is significant enough to have once covered the world in nightmares and to require being sealed away for two thousand years.