Indeed. as I've said before, the Japanese could believe that ANY sword, or indeed anyTHING or anyONE could become demonic if you didn't keep it clean of impurities (blood, for example)
Who here watches Inuyasha? *waits for show of hands.* Guess what? All of the demons in that show were originally born from the impurities of man. Don't believe me? Naraku, villain of the show, was born entirely from the lust of one evil mortal man and some demons he conjured up. "But Aura, those demons make up for all of Naraku's power." Right, and that's why the guy's human heart is what keeps Naraku alive, right?
And I could go on with any piece of Japanese fiction Westerns might be familiar with featuring demons. That's how they were born. The impurities of Man and Kami.