A sword was part of a Japanese officer's uniform. Pretty typical of the 19th century when the Imperial Army was founded (though at that time the IJA and IJN adopted western style sabers) but such was a bit archaic by the 1940s.

In 1934 the IJA replaced European style swords with the Type 94, which was modeled after the tachi, an older style Japanese sword from the feudal era. This went hand in hand with the increasing use of the samurai and their swords as a cultural icon in Japanese propaganda and as an increasingly idealized model for the Japanese martial ethos. The swords were worn by commissioned and non-commissioned officers as a symbol of rank and mass produced for the military (affluent officers could buy a more traditionally made Japanese blade and wear it if they wanted, but such swords were quite expensive). The IJN adopted their use as well around this time but the wearing of swords was not nearly as common in the Navy as it was in the Army if only for practical reasons (not a lot of room in narrow ship corridors for swords).