Mugen Souls takes place in a fictional galaxy with seven worlds using the naming convention of the Japanese 7 days of the week: 日曜界、月曜界、 火曜界、水曜界、木曜界、金曜界、土曜界. The main protagonist is a little Undisputed Goddess, Chou-Chou. She was floating around the galaxy with no memories of her past but the only thing she can recall is that she wants all everything to be hers, especially the 7 Worlds because they were pretty. The main character is able to change into 7 different forms according to her moe affinity without even knowing why she which represent the 7 hues of the rainbow. Being as gullible as she is, she believe that the whole world revolves around her and if something is not her way, she will complain and change it.