You Only Live Twice finds Bond in a slump, unable to recover from the murder of his wife of only a few hours on their honeymoon. He's been eased back into work, but has literally made a mess of 2 missions and M is seriously considering revoking his Double-O status.
The Service consulting physician is fond of 007, and suggests an alternative. He states a man of Bond's psychological makeup cannot rise unless he is challenged against overwhelming odds, so he suggests giving him a literally impossible mission to accomplish and free reign to do it.
Unlike the usual assassination assignments, Bond is asked to travel to Japan and make contact with the head of the Japanese Intelligence Service, a mysterious man of which little is known other than his name; Tiger Tanaka. This is to be primarily a diplomatic mission, and he is to offer to trade British Intelligence resources & information in exchange for the treasure trove of Japan's Russian spy network.
It is thought highly unlikely Japan will work with the British and will be a coup if Bond pulls it off. Bond accepts, and begins his adventure to the Far East; another routine assignment with more than meets the eye, scores settled with Ernst Blofeld, ninja training, and a second chance at life.