Not just that!
How much assistance do you need? Are you wanting to go somewhere specific, or take a tour? How long? Emphasis on cities or countryside? Need more clues. Even if the answer is "don't care", that is a clue in itself.
We did without. Flew with KLM and hit Tokyo, Kyoto and Nara, using Tripadvisor and www.japan-guide.com to find places to stay and do. Citymapper and Google Maps for local maps and public transport. General googling for rail stuff.