When I've compared the Nikko G and Zebra G, what I've found (and I'm sure this could be personal to my hand) is that the Zebra is sharper/more pointed, so it gives finer lines, while the Nikko is slightly more square-cut. I think the Zebra is just a bit more flexible, but it does seem to me, though, that the Nikko is more elastic/"snappier"...it seems to give a sharper transition from thick to thin, which I think could be attributed to being more elastic, or maybe to the slightly squarer cut? They are both so nice and smooth, though...it's amazing how fine they are while still being so smooth-writing!