Faith is a one-handed sword in NieR, received from the mayor of the Forest of Myth after freeing him and the other two residents from the Deathdream. It also can be bought in the Aerie in the second half of the game, if missed.
"A sword carried by the world's most loyal servant. Like that loyalty, the sword's blade is straight and true."
There was a famous singer living in a city in the far east. However, he was no longer able to sing in his later years. A monk appeared by his side out of nowhere and whisper to the singer: “you should pick up this sword.”
“If you kill a single person you’ll be able to sing one song. I you kill two people you will sing two songs. Go ahead and sing some unparalleled songs!” The singer picked up the sword from the monk, hid in the night, and slashed at two bystanders. The next day, the singer can produce beautiful songs, and regained fame and fortune.
Afterward the singer sang a song for each person he killed, and sang two for every two he killed. He continually attained more fame and fortune. However, his desires could no longer be suppressed. If he killed his most important person, what kind of marvellous song would be produced?
And so the singer killed his wife and sang a song. He killed several of his children and sang multiple songs. He killed everyone in his family and he sang and sang and sang. He killed so many people on the streets that he cannot even sing fast enough. He killed and killed and killed and killed. In the end he didn’t sing anything as he killed himself. All that is left is a blood stained sword.