Separate the room gap from the sightseeing plan
Write down the old property’s check-out time and the new property’s check-in time, then ask each property about luggage separately. A room being unavailable does not tell you whether a bag can be accepted, where to leave it or when it can be collected. JR-West’s hotel-storage information, for example, tells guests to contact their hotel about storage before check-in or after check-out; it is not a promise for every hotel.
Keep the things you need during the gap in a small bag: passport, tickets, phone and charging equipment, plus any personal essentials you must have with you. If you might spend a night without the main suitcase, pack for that possibility before handing it over. Decide this while you still have somewhere to open and repack it.
On the evening before a hotel change, pack the main bag and separate the essentials you will need before you next open it. Put the check-out time from your booking beside the first transfer or meeting time, and name where every bag will go. The next morning’s plan needs room for the final room check, taking all bags out and the carrying or handover arrangement you have confirmed. Start the sightseeing plan after that sequence fits, rather than treating check-out as an instant move from one room to the next.