The twelfth article of "Nehan-gyo Sutra" (The Sutra of The Great Nirvana) shows that 'the younger sister called Kokuannyo brings people evil while the elder sister called Kudokuten brings people good luck.'
『涅槃経』12には「姉を功徳天と云い人に福を授け、妹を黒闇女と云い人に禍を授く。」