Hiking mountain like Kaimon dake

Last year I hiked up the Kaimon dake mountain in south west Kagoshima.

I thought it was a good hike for regular hikers, not needing too much equipment. Of course raingear and so on is always good to bring.

Just curious if there are any other mountains like that. If you understand what I am looking for.

Most of Japan is low mountains so there are many. If you want isolated low mountains such as Kaimon-dake, there aren't so many. Most climbs outside of Fuji and the Alps region are just trail hikes, with nothing more than a hiking stick as an option.

If you're talking about southern Japan, the Kirishima National Park has several hikes to the top of some old volcanoes. At the east end of the park is Takachihonomine. It's just a hike up through gravelly ash deposits around the old crater to the summit which has a hut on top.
http://www.japan-guide.com/e/e4629.html
https://goo.gl/HvcxGU
https://www.flickr.com/photos/anaguma/402798322

From the Ebino-kogen area, you can hike up the right side of Karakuni-dake to overlook the eruptions of Shinmoedake.
https://goo.gl/B2n5QA
https://www.flickr.com/photos/anaguma/9117561487

There are several hikes to the summits around Mt. Kuju, north of Aso off the Yamanami Highway.
http://www.japan-guide.com/e/e4775.html
https://goo.gl/tBiiVa
https://www.flickr.com/photos/anaguma/2369640338

There are summits on the west side of Tokyo including Takao-san and in Chichibu NP.
http://www.japan-guide.com/e/e3036.html
There are hikes to the summits in just about every mountain area,
just about everywhere, so a more specific location can get more results. You don't need climbing equipment for most places except in the Japan Alps where even there there are still just hiking climbs available. Fuji is just a hike up except it has weather to take into account.