Sometime in the year 1994 (as humans currently measure time) a beautiful and charming young woman named Sachi came to the attention of a being who lived in celestial court, that being was Susanoo.
(Takehaya Susanoo-no-Mikoto 建速須佐之男命 god of the sea and storms, ruler of Yomi.)
Susanoo fell in love with Sachi and against the wishes of the court and his father Ruler of the gods he traveled to earth and assumed human form.
Calling himself Hanzo he carefully courted Sachi and eventually she came to love him as much as he did she. They lived happily together for over a year then one day their daughter was born.
Unfortunately Sachi was revealed during birth to be an Oni of the Rei clann, Susanoo so angry at her deception killed her still wet with the blood of their child.
Then Susanoo was about to kill his new born daughter when Izunagi father of the gods commanded he bring her to the celestial court.
Angry that his shame would now out for all to see Susanoo hurled her to the ground at his father's feet when he entered the court. Protected by her grandfather's aura from harm she now became a pawn between heaven and hell.
Izunagi revealed his foresight as he picked up his granddaughter and declared.
"Behold your salvation, this child shall be the 奇稲田姫 Kushinada-hime and Orochi's anger abated "
Susanoo was furious, his father was allowing the Aragami Orochi to be reborn? To add insult to injury he'd named his daughter as his sacrifice even granting her title.
Father! Said Susanoo demanding to be heard.
"I refuse, let me kill her now and be done with it, she is not worthy and will fail"
Too late my son, you have awakened the Oni and their dark allies the Aragami to stir even now.
The Oni you so rashly killed has unbalanced the cosmic scale, she was Reihime clan. Now the rice Kami are awakening the Aragami, and all because you killed for pride the mother of your child and their dark princess Sachi no Oni.
The court was against him and so Susanoo submitted though already working on a plot to kill his foe once again.
Taking her to earth she was used to replace the child of a widow who's own had died at birth.
She was a typical school girl with dreams like any other till on her 11th birthday an she was stolen by her father and hidden away in his realm Yomi.
She was frightened when she first came to Yomi till her Oni form emerged. She knew she mustn't eat or drink of Yomi or as legend held she would never leave.
She worried for a bit that she would soon have to eat but was surprised to find as an Oni she could survive long without food or water.
While in her father's house she was told by Susanoo that he wanted her to eat and join her father. She didn't eat no matter how her father raged that she must because she still hoped she could find a way to escape.
An old soul, a woman befriended her and taught her the truth of why she'd been brought to Yomi. She revealed to her that she was the Kushinada-hime and that if she didn't willingly accept her role many or all the people of earth would die or become slaves of the Aragami. That her father was hiding her in his palace in hopes of starting a great war.
The Kushinada listened each day to the woman who came and taught her never knowing she was Izunami the sister and mate of her grandfather Izunagi.
It was revealed to her that who an what she was granted her if not direct command of but at least the ear of both Oni an Kami alike.
It was then on her 15th birthday that her grand father entered Yomi and decreed that her father should release her till her 21st birthday to live once more among the Humans.
Now newly returned to the mortal world she must reside till Her fate is called up an she give herself willingly to Orochi's hunger an be devoured to save all

In this story I'd like to play the Kushinada and you to play as either her Oni or Kami Protector
The Kushinada can of course talk to the Oni an Kami of the world but that dosen't mean they obey.
The Aragami want her dead before their Master Orochi awakens so that the bargin will be broken and war begin so they can claim the earth as their domain.
I will add that there are Oni an Kami as well who crave the war for their own reasons
You will be more powerful than the Kushinada and most of those who want her dead but some will be stronger than you Susanoo can't kill her but he dose have powerful friends