I know its far out, but the KI-61 does look werry simulare to the HE-100. The Japanese did get 3 of them...and here is a small part of the story
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wikki
The Japanese were also looking for new designs, notably those using inline engines where they had little experience. They purchased the three D-0s for 1.2 million RM, as well as a license for production and a set of jigs for another 1.6 million RM. The three D-0s arrived in Japan in May 1940 and were re-assembled at Kasumigaura. They were then delivered to the Japanese Naval Air Force where they were re-named AXHei, for "Experimental Heinkel Fighter".[2] When referring to the German design the aircraft is called both the He 100 and He 113, with at least one set of plans bearing the later name.
In tests, the Navy was so impressed that they planned to put the aircraft into production as soon as possible as their land-based interceptor; unlike every other armed forces organization in the world, the Army and Navy both fielded complete land-based air forces. Hitachi won the contract for the aircraft and started construction of a factory in Chiba for its production. With the war in full swing in Europe, however, the jigs and plans never arrived.[2] Why this wasn't sorted out is something of a mystery, and it appears there isn't enough information in the common sources to say for sure what happened.
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Personaly i belive the Japanese used the HE-100 as template for the construction of the KI-61. They had the license for the engine, was not sure how to implement it, looked at the HE-100 construction and createt the KI-61
That is my opinion...not any historical fact...
found this pretty ok arthicle about the KI-61
http://www.vectorsite.net/avhien.html
LTbear