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Dragonbone Sword in Drakengard 3.
See this sword? It's made from a dragon's fang. That means it can kill an Intoner. Right?
— One to Zero, Drakengard 3

The Dragonbone Sword is Brother One's main weapon after killing Zero.

During a fight with Bartas, one of Gabriella's fangs was knocked loose. One then used it to defeat Bartas by stabbing him.

Later, the fang was forged into a sword and given to One to use against Zero. Since then, the sword has been One's weapon of choice on his quest.