Large oblong trigger guard marks it as a late-production (1939 onwards) Type 14 Nambu "Kyska". Let's hope it's really a 1939 model - those were actually quite well-made weapons, but the ones built after war started suffered a sharp, increasing drop in quality that's largely responsible for the weapon's horrible reputation.
EDIT: Careful examination shows a complete lack of grip grooves. This can mean one of exactly two things: 1) artist was lazy, or 2) Nishi is carrying a "slab" grips Nambu, made after November 1944 as a production expedient. If it's the latter, two words: Poor Nishi.
