The Hokuhoku-sen (full name Hokuetsu Kyuko Hokuhoku-sen) is a train line in Niigata Prefecture operated by Hokuetsu Express. The line operates between Muikamachi Station and Saigata Station but importantly connects with the Joetsu-sen (linking with Echigo Yuzawa and beyond) at the former and the Shinetsu Honsen at the latter.
Hokuhoku-sen Station names and distances from Muikamachi Station to Saigata Station in Niigata Prefecture
Note that some trains go straight through from Echigo Yuzawa, while others require a change of train at Muikamachi Station.
Many people have used this line to get from the Tokyo region to Hokuriku - by using the Joetsu Shinkansen from Tokyo to Echigo Yuzawa Station and then transferring to the Hokuhoku-sen. Just how the opening of the Hokuriku Shinkansen will affect the numbers of people doing that in the long term remains to be seen.