Her name was Lumina

Lumina was the Child of the Moon Goddess, but she was also Sebastian Michaelis's childhood friend. But never did Sebastian think of her as a "friend". He always thought of her as someone he cared for dearly. As children, Lumina's mother forbid Lumina and Sebastian to talk or ever see each other ever again. So, as the years go by and both are at least the same age, they meet again. But Lumina doesn't remember Sebastian, and this causes him to secretly worry.