The series is set in a fictional galaxy of moons that is beset by the "Big Bad", a black cloud that drains the life and color of anything it touches. The galaxy's moons are protected by plantlike children called Moonflowers, who use their emotional states to activate magical "treasures" that are supplied by an infantile being named Little Dreamer, which can then be planted to grow trees that ward off the Big Bad. The series opens with Hanazuki, a newly born Moonflower, arriving on a moon populated by numerous denizens, including colorful rabbit-like creatures called the Hemka. Several episodes focus on Hanazuki's escapades as she learns about her responsibilities and emotions, ending with her growing a Treasure Tree that corresponds with her mood in that episode. As the series progresses, Hanazuki encounters other Moonflowers that have failed at saving their own moons and seek to learn from Hanazuki in order to properly harness their powers against the Big Bad.