He's a demon? I'm assuming the standard methods of dealing with the problem won't work, then. Otherwise you wouldn't be asking the question. Without getting into specifics, all I can say is what I would do. For me, it would boil down to two questions:
1.) Do I have the right sword for the job? 2.) Can I reliably use the sword without hacking off my own feet?
Metaphorical, obviously, but there you go. For what it's worth, if I couldn't answer yes to both those questions, I'd look for other options.