Helel is/was an infernal demon serving Dharkon. Then he rebelled.

as punishment, Dharkon had his followers bind the demon to one of their daughters, an infant named Melanie. The child would be a weapon to smite Dharkon's foes, such as the alien entity Galeem or the Legendaries.

Melanie would not learn of her binding to Helel until much later in life. It's basically a Stand. Or a Persona.