How nerdy is it to put a sharp-edged fantasy knife replica in my kitchen just to cut cheese and maybe vegetables with

Very. Doesn't make it not a good idea, though. What's it a replica of?

Delightfully nerdy

I feel like you've probably crossed the 'terminally nerdy' threshold multiple times over throughout the years, while simultaneously being undeniably cool, so I'm sure whatever kitchen utensils you choose will be just fine

Very cool idea as long as it is actual knife steel or meant to be used! Most of the decorative sword replicas are not, and can shatter or the fail in other ways that you wouldn't expect a normal knife to, and might injure you!

I'd do it.