A Katana Sword and Sheath stolen from a novelty Shop. He sharpened the blade.
It it is not a problem that your character knows how to use a sword, but would sharpening a novelty "for show" katana just be a waste of time? The cheap stainless steel making up the blade is produced to retain the shine and prevent rust; they do not hold edge well and would probably shatter on impact after a strong swing. To me it would make more sense for your character to find a vintage real katana in an abandoned thrift shop and fix that up.
Here's hoping that more people post their character sheets.