Toriko no Chigiri ~Kazoku no Tame ni Karada o Sashidasu Ane to Imouto~

Due to family circumstances, Yakumo Rio and Yakumo Miyu lived in quite a peculiar environment. When they were little, their parents died, and they were raised by their maternal grandfather, who also happened to be the boss of the yakuza, the Yakumo Group.

They were raised in accordance with their grandfather's policy that they should not relate to the group's customs. The sisters grew sound and without any inconveniences. Rio admired the local nurse, Omigawa Kyouko, and secretly made the decision to become a nurse herself. With Miyu, a spoiled child, she spent her tranquil days, however...

A shadow has started to loom over this tranquility. A new rising group, the Mitsuru Group, invaded Yakumo Group's turf, sought to take the group over. The latter was being pushed back under its rampancy when suddenly its boss fell ill and was taken to the hospital. Thus, bad things continued to keep happening, as if rubbing salt into the wound. The Mitsuru Group appeared to be planning to declare that it was taking the Yakumo Group under its wing at the gathering of groups from all over the region, which would take place about a month later, and have all its neighbors recognize this. In such a case, the group would be taken over...

At that time, a man went to the Yakumo Group estate, where the sense of impending crisis grew stronger and stronger. It was Innami Kouzou, the boss of Innami Group, which has been building its strength lately. Innami shared a story with their group, but he made a certain proposal to help. If they presented him with either Rio or Miyu as his woman until the end of the gathering, he would settle the matter with the Mitsuru Group by then. He was kicked out once, but Rio thought about the group's future and offered to be taken herself.

And so, in order to protect Yakumo Group, Rio came to live as a woman of Innami Group's boss. She more or less anticipated what was to come, but what awaited her were days of humiliation far beyond her expectations.
Would it really settle the dispute? 
And what would become of Rio?..

[Translated from the official site]