Mbumba, the rainbow, is a water snake who works his way to the sky by climbing through trees. When he reaches the heavens, he causes the rain to stop. The skies are ruled by Nzazi, Lightning, and the earth is ruled by Mbumba. A struggle sometimes ensues between these divinities: it is a cosmic struggle between heaven and earth.
A myth recounts this epic contest between earth and the sky, between Mbumba and Nzazi; it is a struggle that has to do with the waters, waters that are both life-giving and death-dealing. Mbumba emerged from his watery residence on the earth, and went into the heavens where he visited Nzazi. They constructed a community, but they quarreled when Nzazi insisted that Mbumba remain in the skies to become the guardian of that community. The result of the dispute was that Mbumba returned to earth to the water. Then, some women came to fish in that water where Mbumba dwelled, but the water dried up and they found him. They moved to kill him, thinking that he was a fish. He thereupon bit one of the women, and the water turned red and, like a snake, he moved out of the water and frightened the women. When they had fled, he again went into the sky, and the struggle between earth and sky continued when Mbumba and Nzazi contended over the lives of humans: now Nzazi went to the earth to take the lives of humans, and Mbumba threatened Nzazi with rain if he did so. The struggle shook the universe, as the two divinities sought to demonstrate their independence of each other. On the earth, Mbumba was assisted by Phulu Bunzi, lord of the waters. When Nzazi moved to the earth, it was Phulu Bunzi who caused him to be overwhelmed by water. It was because of this that a pact was reached between heaven and earth, between Nzazi and Mbumba, a pact devised by Phulu Bunzi. And Nzazi then returned to the heavens. So it was that a harmonious balance was achieved between the heavens and the earth, a balance developed within terms of water, with the ruler of the heavens brought under control by the being who ordered the earth. But that balance would forever be a delicate one, and it would have to be regularly nurtured. The relationship between heaven and earth would remain forever contentious, a contentiousness that was also experienced on the earth: later, when Phulu Bunzi was visiting Mbumba, his son died. Phulu Bunzi blamed Mbumba for the death, and consequently killed him and cut his head off.