The Real Touch Marker GM401 by GSI Creos is a 2 in 1 Gundam Marker! In fact, it's equipped with tips at both ends: a large one and a fine one. This way you have the opportunity to work comfortably both on large areas and on small details (and panel lines).
Color is steel gray and ink is water based.
It can be nuanced using the special Real Touch Marker GM400 (sold separately).