The World Falls into Darkness

The plot is that after the deities won a war between demons a few millennia ago, the world entered an era of peace where life and light thrived. But as time passed, the demons grew in power thanks to the corruption in people's hearts. A old, defeated demon wanting to get revenge slips into a weaker deities realm and forces himself onto her to drain her divine power for his own. As he gains power, he would go around defeating and draining other goddesses of their power, plunging the world into darkness.