I work with 3D resources making animations and stuff, So I can say that make it full 3D may be impossible in RPG Maker.
Because 3D assets are special formats, made with special programs, and have to be modelled, textured, rigged, animated, etc... and RPG Maker works based in images, I really doubt that you could do it like a 3D console game. It will be just to heavy.
For 3D games you should use Unity or a similar software.
However, how they said before, you could make your own assets, textured to look like 3D, but it won't be full-3D, you will only give the illusion that it is.
Refering to plugins, you may get one that adds frames to the characters sprites for 3/4 views, and make it in isometric style.