What to do with luggage?

Given that I've repeatedly read that finding room for luggage on the trains can be difficult, I'm wondering what to do with our luggage in the following scenario: we (my wife and I) will be going from Kyoto to Beppu by shikansen train at the beginning of October - staying in Beppu for three nights (9th, 10th and 11th), and then going from Beppu straight back to Tokyo on the 12th. Is it worth the hassle to take our full-sized luggage with us on the train? Will we be able to find room on the train? Does it make sense to have our luggage sent ahead to Beppu (from Kyoto) and then to Tokyo (from Beppu) by takuhaibin? Or should we send our luggage straight from Kyoto to Tokyo? Any advice on the foregoing would be much appreciated.

Or should we send our luggage straight from Kyoto to Tokyo?
This option sounds more logical to me.

How long is your total stay in Japan?

If it is just for those few nights, you can probably get by with a duffle bag or backpack, which shouldn't be too hard to take on the trains with you I would imagine.

If you have only one piece of full-sized luggage, I don't think you will have much problem to bring on board the shinkansen.I have done it with 2 full-sized and 1 mid-sized.

Behind the last row of seats on every car on the Shinkasen, there is space for luggage. You can dump your big bags there and put your smaller duffels or backpacks in the rack above your seat. Trust me, I was worried about the same thing in May, going all over the place with 1 large and 1 extra-large duffel bag, plus a handbag and a smaller duffel.

Thanks so much for all the helpful responses. We'll be in Japan for a total of 15 days, so this is only a portion of trip - so we won't be able to travel as lightly as we might otherwise prefer. But I'm comforted to hear that others have handled this situation successfully in the past. Thanks again!