Dating a japanese sword
Japan early history is highly affected by the influence of the continent and its more ancient cultures.
The culture of the Yayoi period was surely strongly subject to the influence of Korea and thru this peninsula the most important innovations arrived in Japan.
As such, it’s no surprise that the men of Touken Ranbu are all based on something long and hard…plus sharp, as they’re all anthropomorphized swords.
I’ve seen a few in art galleries here and they really are works of art, but I would have loved that up close experience that you had. I was allowed to handle a 300 year old sword way back in the day at Maibara, Shiga, and it weight took me very much by surprise- and realized that unless one has arm muscles like Popeye the Sailor, one isn’t going to flash these swords about for very long as is done in the standard samurai dramas.
There is also the possibility that the mei could be gimei, that is, a false signature. It is a popular theory that 9 out of 10 mei we see by supposed famous swordsmiths are gimei.