Kunoichi... Women who follow the ways of the ninja.
As time passed, they fulfilled their duties, and so they vanished into the shadows of history... or so it seemed.
But even in the modern era, all these centuries later, the bloodline of the kunoichi has not died out.

In the city of Kashiro, in the Kuragami residence, there live four young people.
The Kusakabe twins, Kiichi and Keiji, trained in the ancient Kusakabe-ryuu from a young age, and both are likely candidates to be the next successor.
The two closest to the brothers, also training in the ways of Kusakabe-ryuu, are the kunoichi Yukina Sasanome and Mitsuki Namatake.

The way of Kusakabe-ryuu has many rules that were established long ago.
One rule dictates that a man who studies Kusakabe-ryuu must choose a kunoichi to be his partner and train her, and in turn, that chosen kunoichi must offer her body and soul to him for the rest of her life.

The Kunoichi twins have been capable of wielding kunai since before they even matured into young men.
From the day their training commenced, they had 5,000 days to find a partner kunoichi, and a month from then to teach her the skills of the kunoichi.
Once they have taught their partners everything, they shall hold a wedding ceremony.
And finally they must give birth to the next generation with their partner.

Keiji Kusakabe despises this rule, and is strongly opposed to the fact that his fate must be decided for him.
But despite his resentment, his 5,000 days to find a partner are slowly passing... The final day draws ever closer.

This is where the story unfolds.

[From Johren]