[quote=@Sho Minazuki]
It also doesn't require the Demon's soul to make a Devil Arm.

That's proven by Yamato, Rebellion, and Force Edge, which were all forged from and by the same demon, Sparda. Force Edge was poured with Sparda's power, which allowed Arkham to access his form for a short while before he turned into sludge.

It likely requires immense power to make them strong though, but it doesn't exactly cost the demon's life.
[/quote]

That's true.  I defaulted to making the Devil Arms out of demon souls because that's a parallel between DMC, Bayonetta (as evidenced by Rodin, who does kill demons and make their souls into weapons), and Darksiders (where weapons are literally crafted from the remains of enemies, with soul power evident but not used as a resource).  The company certainly wouldn't have the ability to make powerful weapons without sacrificing a demon's soul.