With regard to step-in crampons there are a huge range available in Japan - any hiking shop should have a good selection. I'm not sure where you're living but if you're in Tokyo check out the gear shops in Jimbocho (there are hundreds there), Ochanomizu and Shibuya. Stores like OdBox, ICI Ishi Sports, Sakaiya, L-Breath etc. There are a lot of Japan-only brands like Mochizuki and Mt.Dax that make good products.
I have 6 point Grivels and 4 point Snow Peaks but I stopped using all of them because I found them completely unhelpful in the mountains. Instead I switched to 12 point aluminium crampons that weighed about the same as the Grivels. If you are on flat terrain 4 points or 6 points may work but the problem with 4 point crampons is that they are in your instep, so unless the points are very long and the ice/snow very firm they don't help much. They don't help at all on slopes or slushy summer snow fields like on Shirouma's "big snow valley". 6 points do work better but can be uncomfortable because they're only under part of your foot - on hard surfaces like ice they can be quite "tippy". We went into Kamikochi in the winter one time and had to walk through the road tunnel which was a solid sheet of ice. One of the other guys had 6 points and it was like he was wearing geta, so he kept tipping forward on them.
If you want good info on a lot of these mountains, check out this site:
The guy who set up the site has 3D maps, gradient profiles and some really good photos, one I use as the background on my computer.