Japanese Sword

[CINDERS]

I forgot to add your going to have to push in the catch with the top hand otherwise it will just catch as expected on the Tsuba, also looks like you do not have a peg but a bolt in your handle the peg can be fashioned out of a light coloured wood with a gentle taper so it fills and fits flush both sides of the hole in the handle.

Trial & error will get you there with moderate pressure to push it in.