Okay. The sword probably is not a period sword from feudal era Japan. However, it is most likely a decently constructed sword. If you go with the walking dead's original timeline (there's been suggestion that the outbreak started in 2003) that would put the sword's ownership starting 1983. As you say her stepdad was very skilled with the japanese sword, I think he'd go for broke and get a blade that was probably hand forged and differentially tempered with high quality steel. So it's a 'real' katana. Is it as great as some of the old blades... no. (*grabs dice to check something*) On average it's a four to five body blade in the hands of a good, strong swordsman. The hamon is not brushed on, and there's probably decent crystallization in the steel. I would say it's got about a standard arc, so it's designed for a balance between cleaving flesh/bone, while still being useful against armor. If Robin's dad was one to frequently practice, his sword is probably based off of later century designs, around or just before the Meiji era. Japanese swordmakers and the samurai had gotten away from extremely detailed and ornate fittings in favor of simplicity and elegance. The main reason is the period was turning chaotic and the samurai needed function over being 'pretty' or over-embellished. They needed weapons that cut well, did their job, and they wouldn't feel bad for dinging up, and weren't so hard to repair. 

Most real steel swords meant to be used in modern times are simple, elegant, but still quite beautiful in their design often going with black finishes for the scabbards and furniture. They tend to feature very pretty steel, with elegant lines and curves, and still pretty sharp. 

So what we're probably talking about is something like [url=http://www.searchfit.org/bugei.com/scart/public/database/product/images_sets/pr1647img1.jpg]this[/url], or [url=http://www.searchfit.org/bugei.com/scart/public/database/product/images_sets/pr1648img1.jpg]this.[/url]

Sorry, I'm a sword nut...martial arts in general, but definitely swords, and the way of the sword. Love European swords too.