On this trip to Kyoto and Osaka, I used the luggage direct delivery service to the airport for both the outbound and return journeys. I recommend using it on your first day at the airport to have your large luggage delivered directly to your hotel. This avoids your luggage inconveniencing others on subways and buses, especially since pedestrian paths in Osaka and Kyoto sometimes have inclines, and dragging luggage all the way to the hotel can be exhausting. For the return trip, it completely frees up your hands, allowing you to enjoy the last day of your journey with just a backpack. You'll even have room to buy more if you wish. Your luggage will be easily retrievable at the airport at your scheduled time. Just remember not to go to the wrong floor or direction; luggage pickup is on the fourth floor of Kansai Airport. Allow enough time to collect your bags before checking in and dropping off your luggage at the airport, then you can continue to shop and explore the airport to your heart's content.