Kunoichi Ryoujoku Zashikirou

It was an act of revenge. She struck at the enemy in their own tower
... but the revenge was a failure.
The enemy placed her in a holding cell called the "zashikiro",
a kind of prison for the insane, but for this ninja,
she knew it would be the place of her death.
Resigned to this fate, her only reason to keep going
was if it could somehow spare the lives of her clansmen.
Five days.
If she could endure the next five days,
her captured friends can go free.

[From DLsite English]