Prologue:

Long ago, during the years ninja began, a clan was founded; the Hart clan. Their kekkai genkai gave them high spiritual energy, enough for them to see things with the naked eye others normally couldn't, which allowed them to see and communicate with spirits and demons such as kitsune, and also seal strong spiritual beings inside of them.

The Hart clan made its fame by signing a treaty with the Zenko [1] which entailed that the Zenko would be safe from harm and the Nogitsune [2], while each member of the Hart clan would have a Zenko sealed inside of them, opening all sorts of possibilities.

The Hart clan's kekkai genkai made them the first and last line of defense, and made them targets for power hungry maniacs. They were soon hired as mercenaries, thugs and assassins, few of them sticking to their old traditions and beliefs.

And their gift turned into a curse during Kurama's attack, where many of their former comrades turned their backs on them and blamed the Nine-Tailed Beast's attack on them. Their friends and allies were few and far between and tried helping them, but it was no use.

In the dead of night, on the 28th of April, 12 years ago, those who blamed the Hart clan for Kurama's attack, snuck into the Hart compound and killed all that they came across; children, women and men. Only when half of the Hart clan had been massacred was the alarm raised, but by then it was too late. The Zenko who were still allies with the Hart clan had fled when the enemy ninja had unknowingly [3] brought Nogitsune with.

On that very same night, Lilian Isis Leandra Iona Thea Heather Hart was born; daughter of Madri and Alex Hart, sister of Zander Hart. But she was stillborn, meaning that she was to be a powerful Hart ninja, if they could seal a Zenko inside of her, but all the Zenko who were free had fled when the assault endangered them.

Madri had a Zenko sealed inside of her, and the Zenko offered to give life to the child, promising to protect her with its life. Madri broke her seal and used the last of her chakra and life force to seal the Zenko inside of Lilith [4]. Her last words were to her son, telling him to take her away and open a portal and to stage his sister's death.

Alex gave his children a head start, holding the enemy ninja off as long as he could, before they overpowered and killed him. Zander used the last of his chakra resorts to open a portal to a different dimension; the portal was in front of a cliff, making it seem as if he had tossed his sister off the cliff and to her death. As soon as the portal closed, he died.

To this very day, everyone believes that the entire Hart clan has been wiped out, but the baby's remains were never found...

Footnotes:

[1] Zenko are kitsune who are considered good and are often associated with the god Inari. They are the enemies of Nogitsune.

[2] Nogitsune are kitsune who are considered evil and are the enemies of Zenko.

[3] The Hart clan are the only know clan that can see them. The enemy nin couldn't see the Zenko or Nogitsune.

[4] Lilian Isis Leandra Iona Thea Heather is a lot longer to say than Lilith, and if you take the first letter of each name you end up with Lilith.