They sell different blades to put them on, but regardless it’s super easy to dull a blade yourself

Then how about an exacto knife? They’re not usually bifl but if you’re only opening letters with it then it will be because the blade can dull

I’ve seen novelty letter openers made to look like samurai swords with the sheath. Might be just what you’re looking for?

My mind went to “the descent” so no judgements here