Cruel Oath is a one-handed sword in NieR: Automata.
"A black oriental sword. Its no-frills design gives it an aura of serious weaponry."
- 9S' default weapon in Route B.
Once, long ago, there was a group of seven boys who were born in the same village. Though they were not brothers by blood, they treated each other as family.
One cold night, a fortune-teller appeared and warned of a traitor among them. The boys laughed it off and went about their business, but the next morning, one of them lay dead.
With each passing night, another boy died. The survivors grew more and more suspicious of each other, each harboring terrible doubts about what happened to their brothers.
[Level 4] Edit
On the morning of the seventh day, a single survivor stood tall. Cleaning the blood from his hands, he chuckled to himself. 'Better go find the traitor!'