If anyone done the zero gravity experience, then you know that you instantly notice the difference in gravity. Your shoulders get more relaxed, your steps feel weird, etc.
Anyhow this seems like NG+ (the manga) atm. Also not sure why era the guy is from since I don't know what the education level was of the warriors in Japan. I don't think someone from the 1200's in Europe would not freak out by a talking sword / being reincarnated. So I am thinking modern Japanese who trained in the art and was possible a solider or a bodyguard???