Like the title says, I'm curious if the Japanese were the only pilots ever to implement this strange technique. I'm referring to fighter pilots only, not other suicide type missions.
There was the Sonderkommando Elbe, which utilized stripped-down fighters to ram Allied bombers in April of 1945. The idea was that trading a single fighter with one pilot for a fully-crewed bomber was a net win for the Germans. When used to ram the tail surfaces, cockpit, or engines the damage could be quite severe. Also, since he was over friendly territory the German pilot may be able to bail out and repeat the tactic in the future.
As promising as this tactic sounds, there were several flaws. First, it was implemented so late in the war that there were sufficient Allied escort fighters to ensure that the damage was not significant enough to discourage future raids. Secondly, new German pilots at this point of the war had little in the way of training so their skills were not at the same level of earlier German pilots (or those of their Allied opponents). Lastly, by its nature the Sonderkommando Elbe was a small experimental force. Their single raid did bring down some bombers, but not nearly enough to stem the tide of the Allies. Even had they had a 100% success rate, it would have been a small victory too late in the war to significantly influence future events.
I found a video of the History Channel's Dogfights that dramatizes the raid in question.
There were also isolated incidents of single planes attempting to ram other planes or enemy targets in both world wars.
Germans used this technique as well. There were some differences. German pilots were trained to ram allied heavy bombers but try to parachute out of the airplane right before the impact. This possiblity wasn't planed for Japanese Kamikaze. Since they were targeting ships it wouldnt make much sense anyways.
The German program was called Sonderkommando Elbe. All pilots were volunteers and got some training, especially on where to hit the bomber for maximum effect and how to approach the bomber pulk. Roughly 20 bombers were claimed destroyed by this pilots. Only one sortie was flown. This happened pretty much at the end of the war and it had no significant effect on the outcome of the war at all.