As far as I remember, before the introduction of Japanese HFs, you can go from the Japanese Army fighter line to the Navy Multirole line, either from the T7 or T8 of the IJA line.
But I checked now and it seems that the two lines have completely broken up now.
Did I remember that correctly? It was once connected? And if it really was changed, would it stay that way and perhaps each of the lines have their own additions?
Asked this because I got my Ki-93 and was hoping that I could go to J7W1 Shinden from there, but it looks like it won't be possible...