ORIGINAL: timtom
In "Japanese Special Attack Aircraft and Flying Bombs", Ryusuke Ishiguro & Tadeusz Januszewski makes no mention of the G4M at all in the Special Attack role, seemingly supporting the above. The P1Y was deployed in some numbers, however, per the authors. Neither of the two Special Attack versions of the Ki-67 are descriped as having been intended for use against land targets, nor, according to this reference, were any of the aircraft specifically designed for that role deployed tactically unless one includes modifications of existing types. The Ki-21 is not listed as a type used for Special Attack.
Rene Francillon claims that as Ki-21s were retired from first line Jubaku (heavy bomber) sentais some of them were used for suicide attacks. I’ve only been able to find one example of a Sally making such an attack however: one deliberately dived into USS Telfair (APA 210) on 2nd April 1945.
After looking at the P1Y Frances again I’ve realised that they were used by several other Special Attack squadrons as well as the Azusa Special Attack Unit I mentioned earlier.