I see a striking resemblance with the Pentel PG305 — there is an upgraded version, the PG505 “Graphlet”, but I doubt Bigraph assimilated that one as well.
Could even be Pilot-esque; besides, I have a Mitshu-Bishi “303” Uni 0.5 with a very similar form factor (pictures soon), but I think the metal tip is slightly different.
Nestler perhaps… See here, for instance: Looking for info on H-58x and H-108x models - #16 by Leonov (apart from the colour, and the clip of course — but mine has been removed — the number of similarities seems pretty high).