Hi there!
On RPG Maker you can use any font you want by default.
What this plugin does, is let you use a font that works like a sprite sheet. Basically, inside the code, the plugin will map your font like this:
When you press A it will draw the bitmap(image) that corresponds to the letter "A" in your sprite sheet. I never tested Japanese, but the plugin has a free version that you can test. I don't see a reason for it not working, but I don't know how the Japanese alphabet works. So is better if you test on the free version first.