Iwaki is Fukushima's big coastal city, spread wide between fishing ports, hot springs, suburbs, and low hills. It is not a postcard town, but it has enough specific attractions to reward a day or two on the Pacific side of Tohoku.
The strongest route links Aquamarine Fukushima at Onahama with the hot-spring and entertainment world of Spa Resort Hawaiians. For older history, Shiramizu Amida-do is the prize: a Heian-period temple hall and garden, and a National Treasure. Iwaki City Coal & Fossil Museum explains why a Hawaiian resort ended up in a former coal district.
Iwaki works best if you lean into the mix. It is part seaside aquarium town, part onsen town, part post-industrial story, and that combination is more interesting than a simple stop on the Joban Line.