Train Reservation using JR Pass

Hi, I'll be making an overnight trip from Tokyo to Aomori from March 24-25th. I have looked at the available trains and so far I'm thinking of taking the 11:20am train from Tokyo Station to Hachinohe Station on the 24th, and then on the 25th I'm thinking of either taking the 11:07am or 12:16pm train from Hachinohe Station back to Tokyo Station. I have read that the trains from Tokyo to Hachinohe require reservations? Do they generally book up? Will I need to reserve in advance, or do you think I will be able to reserve the seats/tickets on the same day I plan to leave? I just don't want to miss the train or be unable to get tickets due to not having seat reservations, but I'm kind of unsure how to do it here/online. And if I do have to reserve in advance online, will I be able to pay using my JR Pass or how will that work? As I'll be purchasing a 7-day pass so I obviously want to use the pass instead of paying out of pocket. Thanks in advance for any help!