A ruby-colored knife carved from dreamstone.
The Ruby Knife is the Masamune's first incarnation in the Keystone Timelines, forged by Melchior and given to Crono in order to stop the Mammon Machine by plunging it into its heart. The resulting skew of energy causes the Ruby Knife to mutate into the Masamune. This raises the question of how the Masamune was created in the Lavos Timeline, in which the Ruby Knife or any other blade was not seen in Magus's flashback as being placed into the Mammon Machine. The common explanation goes that, since Melchior was not exiled in the Lavos Timeline, he had ample time to finish the Masamune in its final form.
Translation: Red Knife