Before boarding from Tokyo to Kyoto or Shin-Osaka, choose a place your suitcase can use. A bag's size, its handling and permission to use a space are separate checks.
Four places with different conditions
Check fit and whether you can safely lift and lower your bag.
Keep your bag within your space and the aisle clear.
Some storage is available without reservation on a trial basis. Oversized suitcases still require the corresponding reserved seat.
For passengers with the corresponding booking. The area is shared among its reserving passengers.
Simplified illustrations, not a seat map or a dimensioned model. Facilities and layouts vary by car. The drawings do not show storage capacity.
“No reservation required” does not mean “space guaranteed”
Check your bag and your train's facilities. A suitable place may already be in use. Do not assume an empty reserved area is available to you.
Think about lifting as well as size
Try handling the packed bag before travelling. If it is awkward, plan another suitable storage option or compare forwarding. Keep frequently needed items accessible without repeatedly moving a large suitcase.
If you cannot find suitable storage
Ask the onboard staff for guidance. If another bag occupies the area linked to your reservation, keep your booking details ready. Avoid moving unattended luggage yourself.