You mean, would it have been like D-Day? Hard to say, really, as it didn't happen and it's kind of a counter-factual. I don't know much at all about D-Day, the plans for invading Japan, or WWII military history in general, but there are some things to think about:
The Japanese, as I understand it, had a history or dying rather than giving in, so there may have been civilians and soldiers committing suicide and/or going down while taking as many Allied soldiers with them as possible.
How would the coastline of Japan differ from that of the Normandy beaches? Is it even beaches, or is it cliffs, bluffs, shoals, or marshland? That will certainly make a difference in how your soldier experiences things.
What are the Allied soldiers' feelings towards the Japanese, as compared to the Germans? Do they think they're evil, like the Nazis are evil? Again, this will affect your character's feelings and actions as he lands.
As far as Saving Private Ryan times ten . . . I don't know particularly why this invasion would be ten times more intense than that (can it be that much more intense?), but if you have particular reasons to think it
would've been ten times more intense, and you think you can pull that off, then by all means, have at it. It's a what-if situation, so no one can say you nay. That being said, the answers to the questions above might help you think about exactly how/why such an invasion might have been more intense than D-Day.
Good luck!