Luggage forwarding is often presented as one of Japan's small miracles. It can make crowded stations, stairs and train changes much easier. But the useful question is not only how to send a suitcase. It is what you will need while it is somewhere between two doors.
This note began with a question I repeatedly see travelers asking. The answer is my own, shaped by living in Tokyo rather than by a list of search results.
Send what can arrive later. Carry what tonight depends on.
Begin with the place receiving it
Before filling in a delivery slip, ask the next accommodation whether it can receive luggage before check-in. Confirm the reservation name, arrival date and any instructions they want written on the label. A hotel with a staffed front desk can usually explain its procedure. A private rental without someone to receive the bag may be a different matter.
Routes, cut-off times and delivery conditions change, so I would trust the staff handling the bag more than an old social media post. If the timing is tight, build in more room or keep the suitcase with you.
Pack for one ordinary night
Keep your passport, medication, valuables and anything irreplaceable with you. Then add the unglamorous things that make an evening easy: a change of clothes, chargers, sleepwear and whatever the weather may require the next morning.
This is not pessimistic packing. Delivery can be affected by route, traffic or weather. A small overnight bag means a delay remains an inconvenience instead of taking over the trip.
Use the lightness you created
The best part is not the service itself. It is arriving at a station without wrestling a large case through the crowd, taking a staircase without calculation and stepping into a small café without wondering where your luggage will fit.
Try not to fill that freedom with three more attractions. Let the lighter day feel lighter. Walk the neighborhood around your next stop, have dinner before check-in or notice a place you would have passed while watching your suitcase.
Luggage forwarding works best when it is not an act of faith. Send the weight ahead, and keep enough of your evening close.