JR East released 2024 lowest ridership lines list.
https://www.jreast.co.jp/press/2025/20251027_ho01.pdf

I tried to make a list, but LibreOffice™ Calc™ is Fucking Retarded™ and keeps converting some numbers into dates in an irreversible manner even if I explicitly turn formatting off. All I can tell is that the worst section is the Naruko-Onsen - Mogami section on the Rikuu East Line at 31 passengers per day.