Well, you are only "silvering" half of the Katana's single edge. That would mean that only about half the stress dealt should overcome the catch (i.e. half the wound on a fae would have iron-induced burns).
Also, to make a really, really cool sword, find a meteor with very high iron/nickel or iron/iridium content (commonly known as meteoric iron). Make a fairly large silver parabolic mirror to make a solar furnance and forge your meteoric iron into a sword using only daylight. Quench the sword during forging into Holy Water, and coat one of its two edges with silver taken from your grandmother's kitchen set you inherited. Give the sword a cool name and inscribe many religious symbols on it. Regularly treat the sword against rust/wear with Holy Oil.
So... silver and iron edges (fae/shifter bane), of meteoric origin (giant/dragon bane), forged in sunlight and holy water (undead bane) and made into a potent symbol of faith, wielded by a (presumably) true believer (outsider/demon bane).
Did I forget any major supernatural group?