Fuyu-Syogun is a beautiful medium grey which leans blue. It is a light or pale colour, with good saturation. It does well on blank paper, but the writing gets somewhat lost when using lined or grid paper, even if the ink lines of the ruling are faint, especially when using thinner nibs. I like it most on white paper.
Despite it being a light ink, there is some ghosting on thinner papers, as it is fairly saturated. I’ve observed no sheen; some shading is present, from very little to pronounced, depending on pen and paper combo. I’ve seen no feathering, no bleedthrough. Fuyu-Syogun has great flow and coats the nib well. It replaced my J. Herbin Gris Nuage: it has the same tone, is more saturated, doesn’t dry flat, and is definitely more usable for daily writing in a wet nib: it does very well in my Sailor 1911L 21 kt H-B as it gives me a nicely saturated, crisp, contained line, and dries quickly.
To my eye, both Iroshizuku and Fuyu-Syogun and Kiri-Same are greys that lean on the cool side, the first, bluer, the second, more purple.