Standing seats on Hayabusa? JR Pass

Hi,
Using the JR pass, I learned you must have a seat reservation using the Hayabusa shinkansen trains to Tohoku. But I also heard you can buy standing tickets. Can I do the same with JR Pass? Or do I have to combine it with a seating ticket to be allowed to ride?

Standing tickets are only available when all seats in Hayabusa are sold out. The ticket will indicate in which car number to stand.

The direct answer to your question is yes, you can buy standing only tickets with your JR Pass. No need to combine with a seat ticket. And previous comment is correct, standing tickets are sold only when seats are sold out, which is possible but unlikely, especially if you are travelling alone.

It have occured to me a few times that the Hayabusa trains were full, having to take a later or "slower" train. I assumed that the big red X mark on the train departure list meant "no go" so I did not bother standing in a queue.

I think I actually tried to make a seat reservation with the JR Pass on such a train (did not know the seats were gone) but the staff member said the train was full.

But... it is not possible to just walk onto the train without any seat reservation at all (standing or non-standing) and just hanging around in the entrance area?

I always try to make reservation in advance but sometime I have tried to return back earlier.

sold only when seats are sold out, which is possible but unlikely, especially if you are travelling alone
Unfortunately the Hayabusa does sell out, and probably more often than the previous poster realizes. It does depend on time of day and day of week.

it is not possible to just walk onto the train without any seat reservation at all (standing or non-standing) and just hanging around in the entrance area?

I did it once, when the train was fully booked, with my JR pass, not knowing then that I could book a standing ticket. The inspector walked past me, no question asked.

it is not possible to just walk onto the train without any seat reservation at all
It is very easily possible. I accidentally caught a train with reserved seating only and found a spare seat, and didn't get the opportunity to pay for the reservation fee (a few hundred yen). For that particular service I wasn't aware before boarding it was fully reserved.

There are some fully reserved trains that do not actually require a reservation and one example is the N'Ex for JRP users (despite the announcements - the detailed rules are different), so there are exceptions.

The N'EX does not currently require a reservation for anyone, JRP or not. Non-JRP users can purchase a so-called "non-designated seat ticket" (ΐΘ–’Žw’θŒ”), which essentially works like a non-reserved seat ticket (allows using any vacant seat on any train on a given day).

So... To conclude this. Having a national JR pass it would be fine getting onto a reserved seats only train like Hayabusa but standing during the journey?

(I would not dare sitting on an empty seat unless it was just for one stop to avoid any embarassing moments...haha)

On some trains (not the Shinkansen), reservations are checked before boarding. Other than that you are probably fine, it's not like you are riding without paying so nobody will care.

So... To conclude this. Having a national JR pass it would be fine getting onto a reserved seats only train like Hayabusa but standing during the journey?

No, as PPs and this webpage https://www.japan-guide.com/e/e2018_tohoku.html says a reservation either for a seat or a standing place is required to ride the Hayabusa:

gThe Hayabusa is one of the few shinkansen trains without non-reserved seating. A seat reservation is mandatory. When all seats are booked out, standing tickets can be purchased.h

Japan-guide is not an authoritative source, however. Just for fun, look into the “Α’θ“Α‹}Œ”.