I don't think we will ever find out Rudeus' original name when he was a 30+ year old Japanese male NEET. I think his name will be one of those things we never find out since he is supposed to guve he reader the potential to better assimilate themselves in his shoes. Without a real name ever actually given, the reader can imagine themselves as Rudeus better than if he had a name since there lies a possibility we could become him, someone who was reincarnated into another world. A big contrast from Re:Monster where they give him a name, so we can't claim in our subconscious as easily to be the main character. Do you think we will ever get a name? or will we never get a name because it is better that way? I personally think the author will never give a name.