Arianrhod (“silver wheel”, thus, the moon), is one of the descendants of Don. She had two brothers, Gilfaethwy and Gwydion the sister of Math ap Mathonwy, whose quality was that he required a virgin’s lap to place his feet in, unless he was at war. When this virgin was raped, Math asked for a replacement, and Arianrhod volunteered. But when she stepped over his rod, she immediately gave birth to two children: a young boy and a blob. (This is likely because the word morwynmay mean either ‘virgin’ or ‘free young woman’, but it also indicates her divine status.)
The boychild was named Dylan; he was a sea-being who returned to the waves. The blob was snatched up by Arianrhod’s brother Gwydion, who hid it in a chest until it grew into a baby. Arainrhod imposed three geases upon this boy: he would have no name unless she named him, he would bear no arms unless she armed him, and he would have no human woman to wife. Thus, Arianrhod denied him the three essential passages to manhood. Nevertheless, Gwydion raised the nameless boy, and one day Arianrhod spied a young boy killing a wren with a single flung stone. She called out that he was a bright lion with a sure hand, and thus he took that name: Llew Llaw Gyffes. Later, Gwydion faked an alarm, and tricked her into arming the boy.