Many thanks to everyone for your answers to my questions.
I'm glad to learn that it was an army sword and an army private as I could not fathom how a naval officer could have crossed paths with a corporal from 43rd Inf Div out in the muddy jungle.
One could speculate forever why Private Seiichi had an officer's sword. Perhaps he was the ranking survivor of his company and was leading a banzai charge with his dead commanders sword. The only people who know the answer are no longer able to tell us.
George, the tassel hung from the sword handle for many decades, standing in a closet in my parents house. It had become so fragile that it was sort of crumbly to the touch, so I put it in a little box. That's where the folds that you noticed came from.
I don't think the blade is traditionally made. It shows no signs of grain (hada) nor temper line (hamon) that I can see. I took several pictures of the blade, but the pictures did not turn out very good. I will attempt to remove the tsuka some day when I'm feeling lucky. Until then, caution is the better part of valor.
I hope someone can tell me what the material is on the scabbard. One website said it's ray skin. The material under the ito is also ray skin, right? They sure don't look alike. I've never seen a stingray, so I don't know if they have such vastly different textures.
Again, many thanks for answering my questions and thanks to the owners for allowing me to ask my questions here. Hurray for the internet!