Is the Russian website the only source for that info? It's always a good idea to get at least another source for that kind of info. The web link I sent has a pretty good amount of Japanese aircraft pics and I have not been able to find something that they did not have a photo of. That being said, it could be one of those that very few know about or even a test aircraft design, etc. But a secondary source for the info on the upward firing guns might me a good idea.
No, on the contrary, from what I understand from that page, it seems that no weapon was upward firing. I don't remember where I read about the gun. I was looking for a photo to confirm the mounting.
I have three references on the D4y. All three mention limited use as a nightfighter, one goes into a little more detail mentioning 2 x 20 mounted behind the pilot firing at an oblique angle but I am afraid no picture. It does say however that only a small number were used and that they were all inline (Aichi Atsuta 32) powered versions.
Records of the 210 ku based at Meiji indicated that they had 5 D4Y2-S "Suisei Nightfighter" on strength. These aircraft were involved in interception of B-29 raids in 1944. However, it would appear that the missions were flown during the day (e.g. ~3PM Feb 10, 1944).
Maxs75 the night fighter version was also used by the 302Ku as shown on the box art.
Will a photo showing the actual victory markings suffice?
I have additional photo's that show the Judy carried a single upward firing 20mm cannon. Will post a couple of shots on the weekend if I can get my scanner woking again.