The Ki-45 Kai-Otsu, otherwise designated as Type 2 Two-Seat Fighter, Improved Model B (Otsu/乙) (二式複座戦闘機 乙型), was the second production variant of the Ki-45 series. This version was a simple bomber-interceptor modification of the Ki-45 Kai-Kō, replacing its 20 mm cannon with a Type 94 37 mm gun, the same model used on the Type 95 Ha-Go tank. However, because it was originally a tank gun, the rear gunner had to manually reload each shell, resulting in a slow rate of fire.

It was introduced in Update 1.31. Although it offers a similar gun loadout to the Ki-45 Kai-Kō, the 37 mm cannon is far less effective due to its limited ammunition, very slow rate of fire, and severe drop-off caused by the short barrel. This makes the Ki-45 Otsu a challenging aircraft to use effectively, as it behaves more like a heavy cannon aircraft, similar to the Hs 129, Ki-109, or P.108A, but without the benefits of a large-caliber weapon. While it does feature an APHE shell, it suffers from the same difficulties when engaging aircraft, further compounded by the weak penetration power of the Ha-Go's main gun.