When it became apparent that Germany was never going to be in a position to invade India, the Germans dumped him on the Japanese.
The Japanese formed an Indian National Army from prisoners of Indian Army units captured in Malaya and Singapore, which are being used in this offensive.
Bose had some crazy idea that if the Japanese could get on Indian soil he could spark some kind of uprising against the British. Of course, seeing how Japan had dealt with other countries in its "Co-Prosperity Sphere," the Indians were even less enthusiastic about the Japanese than they were about the British.
Local commanders were decidedly pessimistic about the operation, but high command and Tokyo made them do it. The Times map reveals the same thing a modern satellite map shows - Imphal is surrounded by miles and miles of rugged, heavily forested terrain with an almost nonexistent road net in 1944. It's perfect terrain for defenders. Even if Imphal had fallen, many miles of this terrain stood between the Japanese and the Bengal plain. It was a doomed operation. Between casualties of war and disease and malnutrition, the Japanese Army ordered into the attack was destroyed as a viable fighting unit.
Burma was a cheap satellite for Japan. They only used four divisions to take it, and added a fifth later. It was the roadblock to effective supply to China and a roadblock to the British thinking about retaking Malaya, Singapore and threatening the NEI. The five divisions have been steadily holding out for the past two years. It’s a strategic keystone to the western end of their Empire, and it only cost them five divisions.
Now the Japanese decide to throw them away with the stupid invasion of India. As you pointed out, there is absolutely no logistical support for this invasion. The terrain that made it so easy to defend Burma also makes it bad as an offensive base. The Japanese divisions will starve to death at Imphal, and from that time on the Allies will have a much easier time re-occupying Burma.
And you make a good point about the starvation situation and Japan’s Indian “allies.” If the Japanese soldiers are starving, what do you think they are giving the Indians as rations? If anything, the Japanese are looking at their Indian allies as “livestock.”