i have studied fencing, Medivel combat, and a little (midgitated little) amount of bushido. from a practical stand point it does sound silly. all the reasons why have already been said.
however, thats where super human strength, magical encantements, mithril (wonderful for weapons that would otherwise be too big) and elven swords smiths from a forgoten age come in.
Make it light, make it strong, and make your MC strong, and it may work.
but back on the practical, most stances start very close to the body, so that you can hide your starting motions. so a large sharp bulge would be bad for you.
you could make it a one handed weapon, a sheild that is strapped to the arm, with the bottom curve of the sheild sharp and a long or bastard style blade protruding from the edge.
this poses its own problems.
(going to stop self before rambling begins)