Short answers, pulled from the story.
Operation U-Go aimed to capture Imphal and Kohima in northeast India, severing Allied supply lines to northern Burma and cutting off the air route supplying Nationalist China. Lieutenant-General Renya Mutaguchi also intended to advance to the Brahmaputra Valley to exploit any collapse of British authority in India.
Lieutenant-General Renya Mutaguchi commanded the Japanese Fifteenth Army, which carried out Operation U-Go. The broader Burma Area Army was under Lieutenant-General Masakazu Kawabe, and the operation was ultimately sanctioned by Field Marshal Hisaichi Terauchi and Prime Minister Hideki Tojo.
Mutaguchi gambled that early battlefield success would resolve the supply difficulties before they became fatal. His divisional commanders believed this was reckless, and several staff officers who voiced strong opposition were transferred before the operation launched.
Two brigades of the Indian National Army, the armed wing of Subhas Chandra Bose's Azad Hind movement, were assigned to the attacks on Imphal from the south and east. Japan had originally planned to use the INA only in auxiliary roles, but Bose persuaded Japanese commanders to give them a direct combat role.
British and Indian forces suffered around 16,987 dead, missing, and wounded. The Japanese sustained 60,643 casualties, including 13,376 killed. Most Japanese losses resulted from starvation, disease, and exhaustion rather than direct combat.
Mutaguchi formally called off the offensive on the 3rd of July, 1944. He was dismissed on the 30th of August after having already sacked all three of his divisional commanders during the retreat. Lieutenant-General Kawabe, whose health collapsed, was also removed from command.