Fukuoka to Tokyo on Shinkansen?

I will be flying from Tokyo to Fukuoka for 5 nights. I have given thought to taking the shinkansen back to Tokyo as I will have a 1 week green pass. I'll have a large suitcase with me. It's big and awkward but it does fit in the overhead space with a couple inches of overhang that I took on a previous Nagoya-Tokyo trip. Does that sound like a nightmarish journey and I should just fly back?

Any reason to take the shinkasen? It takes somewhat longer and has small windows with not much to see like airplanes.

Green Japan Rail Pass?
Are you a bigger person?
I guess Ordinary Class cars of Shinkansen trains are suitable for most people.

The gap in the prices of the 7-day Green pass and the 7-day Ordinary Class pass is about nine thousand yen, which sounds enough to send three to five parcels from Fukuoka City to Tokyo�fs urban area by a major delivery service.
https://www.japan-guide.com/e/e2278.html

Japan Rail Pass does not allow you to use Shinkansen Nozomi or Mizuho train service.
You can take a Sakura train from Hakata until Shin-Kobe then a Hikari train to Shinagawa or Tokyo, which requires about 5 hours 50 minutes (including waiting time).

How about making one or a few side trips?
e.g.
Miyajima Island
(from Hiroshima Station, with one train and one ferry rides),
Himeji Castle (from Himeji Station),
Hakone (from Odawara Station).

Shinkansen is 6 hours, but you leave and arrive in the middle of the city and there is no security or luggage check/pickup. With JR pass, you have to transfer in Kobe or Osaka as you can't take the Nozomi train, so that does add a little hassle. .

Plane is under 2 hours, but you have to add at least an hour on both ends for airport transfer and time through security. So I'd plan on at least 4 hours (+1 more if you flew to Narita vs Haneda).

Time vs hassle vs money decision, really. I'd probably ride the train if I was already going to have a JR pass. 2 hours isn't much, you won't have to deal with the airport, and the train seats are much bigger with more leg room.

you have to add at least an hour on both ends for airport transfer and time through security

No, you don't. Fukuoka airport is 6 minutes from Hakata station, plus at most 30 minutes at the airport and some wiggle room, you're well under an hour. On the Tokyo end it depends where you go in Tokyo.

I�fm not a person of size I bought a green pass last year and I really enjoyed the bigger seats and it was less crowded. I had that large suitcase and being in a bigger space and less crowded carriage I was more comfortable having my own eyes on it. I used Takyubin but they trashed my luggage so if I can put it on a train with me it�fs better (same with airline).

I will have a side trip from Fukuoka to Kagoshima and once in Tokyo I will visit Nagano and Matsumoto. The pass does have other purposes so I�fm thinking why not use it on the way back.

In Fukuoka I will be staying near Hakata Station and in Tokyo I will be staying in Akihabara area.

I have done this trip & it was fine, a long day on a train but fine. I cycle & walk a lot on holiday so it was a relaxing day off. I had the three week Jr Pass so it wasnt a hard decision. As you also have a pass you have to decide what is more important, the cost of the flight or the extra time taken. If the trip is a shorter one then I would fly to get an extra half day in Tokyo. I have flown that route as well & that was great too.

Why not visit Nagano and Matsumoto on the way between Hakata and Tokyo?

I've done the same trip a few times. I just use it for a rest day, and visit say Akihabara at night. You can also change at Okayama, as that is where most of the Hikari to Tokyo start from.

(+1 more if you flew to Narita vs Haneda).
Haneda can be a pain, and really not necessarily that much faster into the city - I would give it a 30 minute advantage over Narita, but most of the time when I do airport transfers from Narita I don't have to change trains as my destinations are Tokyo, Shibua or Shinjuku.
From Haneda the trip often involves several trains or the bus (and Tokyo traffic).
OP is going to Akihabara so with the skyliner from Narita or coming in from Haneda they are about even in travel time (53 vs 43 minutes).

Can't visit Nagano and Mastumoto on the way back to Tokyo because there are no large enough lockers for my luggage. I would have to get a hotel there and it takes longer to travel Hakata - Nagano than Hakata - Tokyo. I was hoping a few others would post their experiences on this route so thanks.

Trip is 2 weeks.
2 Nights Tokyo
5 nights Fukuoka
7 Nights Tokyo

I�fm assuming that there�fs some really pressing reasons that necessitate you having to travel with luggage which is so big that it doesn�ft fit in a locker?

(I�fm not sure I can even imagine a single person travelling with luggage so big that it won�ft fit in a locker. Is there some really large thing that you need to carry around with you which requires a steamer trunk? Forgive me if it seems that I�fm being nosy, but my imagination is running away with me, trying to work out a possible situation which fits your facts ;0))

I did it with a large suitcase & a bicycle in a box. It was a good relaxing :)day. I read a book & ate ekiben :)

It's a 30" duffel bag/suitcase max size for airline checked luggage. When I did look for lockers I couldn't find a big enough one so I carry it from train-hotel-airport. It's not very difficult I've taken 3 trips to Japan and dozens of domestic USA trips I have grown accustomed to it.

Not sure where that extra smiley came from, anyway. This is what I had look at the dimensions! http://www.bike-cases.co.uk/product-bike-box.php

30 inches?
I�fm assuming that you mean that�fs the length of the longest side?
Max size for CHECKED luggage?
Don�ft understand that.
There are certainly luggage lockers that will fit that.
A large locker will fit two medium sized cases and an additional small bag. Our family of 3 on a 19 day trip often out all our luggage in one large, or two medium, lockers at JR stations.
Backtracking from Tokyo to Nagoya and Matsumoto because of your luggage- rather than visiting those places en route from Hakata to Tokyo is an unusual choice to make.

I'm guessing that went behind the last row or in front of your legs? Too big to fit in the overhead space. My bag is 30"x16"x16".

Have you considered a more regular sized bag? Or two smaller ones?
It seems that your whole holiday is being dictated by the size of your luggage.
Even if you need 30x16x16 cubic inches of stuff, there are so many ways you could do that more conveniently.
(And in any case I�fm sure that large lockers are 16 in wide so I really can�ft see how even your existing luggage won�ft fit in one)

Have you considered a more regular sized bag? Or two smaller ones?
It seems that your whole holiday is being dictated by the size of your luggage.
Even if you need 30x16x16 cubic inches of stuff, there are so many ways you could do that more conveniently.
(And in any case I�fm sure that large lockers are 16 in wide so I really can�ft see how even your existing luggage won�ft fit in one)