From Fukaura we opted to pay the 500 yen reservation fee and use Shirakami Resort liner - which runs three times a day - to go to Goshogawara. There is a standing nebuta museum there which Hiro's parents wanted to show me. The highlight of the building was the view from the top floor - Mount Iwaki was being uncharacteristically agreeable and was not hidden by clouds. Most times I have been to Hirosaki I've not been able to see it, even though it's on the outskirts of the town.
We took a regular train back from Goshogawara to Hirosaki and changed for a train to Odate. A loooong day but very scenic. For anyone using seishun 18, unless you want to go straight through without stopping, it may not be worth using a day's pass. At any rate, study the timetable carefully!