IJAAF & IJNAF wrecked aircraft #6 - Various

The aircraft in the video clip today are a bit difficult.

First of all the fighter in the foreground is a "Hayabusa" (Oscar). The 3-blade propeller and the multi exhausts indicate that it's a Model 2 Kai. Unfortunately, no tail marking is visible. Note the unusually thick IFF lines.

We have more information about the aircraft behind it, but it's still a bit mysterious. The tail marking is "931-21" and is a Nakajima B6N "Tenzan" (Jill) equipped with "3-Shiki Type 3 air-to-surface radar" (a.k.a. H-6 Dentan or Ku6go Dentan). The tail number would indicate that the unit the plane belonged to was the 931Ku.

The unit was organized on February 1, 1944, to train crews and maintain airplanes for escort aircraft carriers and for anti-submarine patrol missions. The unit was  mainly equipped with Nakajima B5N "Kate" and "Tenzan" but also trainers. During the Okinawa campaign, they flew night torpedo attacks against enemy ships.

The problem is, according to all Japanese sources, the 931Ku used the tail marking "KEB". So, either they changed the unit marking during Okinawa (more probable) or the aircraft belonged to an unknown attack unit (kogeki-tai) (less probable). 

The last aircraft in the video with the partial tail marking "71" is rather difficult to identify. Any ideas?