Leszek A. Wieliczko's Ki-84 book (ISBN: 83-89088-76-2) states the following about the KI-84c:
"Even more heavily armed was another version designated Yon-Shiki Sentoki Hei-Gata, i.e. Army Type 4 Fighter Model C, or Ki-84 Hei (KI-84c). This time the Ho-5 cannons were retained in the fuselage (like on the Ki-84 Otsu), whereas the wing-mounted cannons were to be replaced by new 30-mm Ho-155 II cannons (sometimes incorrectly referred to as Ho-105 or Ho-115). In fact, the Ho-155s were usually not mounted, as their development never reached a stage allowing quantity production. Reportedly, there were several cases of only one Ho-155 II mounted in the starboard wing, but there are no photographs to support this claim. (Some books contain a photograph captioned "Ki-84 Hei" but it was infact a Ki-84 Ko no. T2-302 captured and tested after the war by the Americans; the mistake results from the fact that the aircraft had long and thick fairings of the wing-mounted cannons, which implies weapons of a much greater calibre.) The Ki-84 Hei practically remained an experimental machine."