Battosai

Apologies, trying to post all the pictures I have but it won’t let me post most of them.

Hello everyone, My grandfather passed and left me a Japanese sword he acquired during WWII. Unfortunately, I never got the chance to sit down and talk to him in length about the sword, I only have a vague story from my father about my grandfather being primarily in the Pacific during the war, in the Marines. As the only other Marine in the family, he left me the sword and since then I’ve tried doing my own research. However, I can’t seem to find any definitive answers as to whether or not it was a “family sword” made into a military service sword or if it was some kind of forgery, the signature on the tang says “Tadayoshi” according to Google. But I’ve been told it’s on the wrong side, but others have said it may have been put on that side and could still be legitimate. Needless to say, I’m at a loss for what exactly I have here. There is also some kind of yellow/white marking on the tang that I can’t find any information about. I will attach photos, any info that could help would be greatly appreciated!