Ive never seen any Japanese 6 engined bombers. They did have the Nakajima G5N Shinzan http://www.combinedfleet.com/ijna/g5n.htm
and Nakajima G8N Renzan. http://www.combinedfleet.com/ijna/g8n.htm
Both were fairly large 4 engined aircraft.
The Germans had the Messerschmitt Me 264 that looks very close to a B-29 with the fully glazed nose and 4 engines. It had a wingspan almost as big as the B-29 but the fuselage was a lot smaller. There was also a 6 engined version of the Me 264 http://www.luft46.com/prototyp/me264.html
Germany also had the 6 engined Focke-Wulf Ta 400 in the works.
http://www.luft46.com/fw/fwta400.html as well as the Messerschmitt Me P.08.01. The P.08.01 was a 4 engined pusher flying wing with a huge bomb load and huge range!! http://www.luft46.com/mess/mep08.html
The hiryu was the Mitsubishi Ki-67. This was a twin engined medium bomber.
Fighter pilots make movies.
Bomber pilots make history.