Reserving seats on the Shinkansen

Can I reserve seats on Shinkansen before arriving in Tokyo at all? We will go from Tokyo to Hiroshima with large suitcases and were hoping to get a back seat to put our bags behind the seats. Thanks

If you live in United States, Singapore, Australia, Malaysia or Hong Kong, you can download a smartphone app that allows you to make reservations:
https://www.japan-guide.com/e/e2018.html
https://smart-ex.jp/en/

Note that Japan Rail Pass users cannot use this app to make reservations, though.

You dont need the back seats to use back storage space. Just be the first ones on the carriage and place them there.

If there is already bags there, which tends to be highly rare. Then lift those bags and place your underneth those bags.

Best to board the rear door so you can access the area first.

If there is already bags there, which tends to be highly rare.
Quite common, especially on Hikari and Sakura trains. Less common on Nozomi.

Maybe I've dodged the busy trains then. I tend not to use the train between 10am-3pm as the are full of more tourists. Hence why I probably haven't had issues with luggage storage.

But I did have a train once. And a local gave me the same advice about luggage as I passed on.

I have travelled with a bicycle in a box and have generally been able to use the storage space without problem. I have on occasion had to stand in the part between carriages with my bike for at least part of the journey although that hasnt been that common. Standard size suitcases will fit on the overhead racks which reduces the number of people using the space behind the last set of chairs.