Once, there was a boy named after the god called Nabu. He lived in a small house with his parents, and his sister, Ninlil (after a goddess) who always caused trouble. He had a best friend, named Sin (also after a god), who loved to adventure with him.
She turned into Ninlil!
Sin and Nabu noticed that Ninlil was always going into the forest. So one day, the decided to follow her.
You shall defeat the evil demon Lamastu.
They followed her into the forest into a clearing, but stayed well behind as to not be spotted. They looked into the clearing, but Ninlil wasn´t there. Instead, they found the female demon Lamastu plotting with the god of plague, Nergal.
SIN AND NABU!! OUR HEROES! YOU DEFEAT THE EVIL LAMASTU
They decided to stay until Lamastu left, and when she did, she went the same way that Ninlil came in. They followed Lamastu back through the forest, and saw her transform into Ninlil.
They jumped out and fought her, and just when she was about to kill them, they prayed upon Ellil, who helped them kill Lamastu. The dead demon stayed inside of the body of Ninlil, but looked more like the demon. Sin and Nabu brought the body of Ninlil back to Nabu´s parents.
They realized Lamastu had been influencing everything Ninlil had been doing, and eventually became her, but stayed in the same body, able to transform back into the demon´s body at will. Everyone in the village declared Nabu and Sin heroes.