There is no porter service at Japanese stations. The major stations have escalators and lifts but the small stations only have steps. If you are going on a trip lasting one or two days, you can use the Takkyu-bin luggage-sending service for a modest fee to have your luggage delivered to your destination.
Example: You are departing from Kyoto for Tokyo and want to spend 2 nights in Takayama and Kanazawa. For those 2 nights you can keep a minimum amount in a bag and have your suitcase delivered to your hotel in Tokyo.