At the end of WW2, did Emperor Hirohito volunteer to stand trial for war crimes? Was he planning to plead guilty? Did the US refuse all this?
Please make a citation because I would like to read more about this if at all possible.
You appear to be asking about the account General Douglas MacArthur gave of his first meeting with the Shōwa Emperor. During that event, Hirohito assumed full and sole responsibility for all of Japan's wartime actions, and offered himself to the "judgement" of the Allied powers.
Trials are for determining guilt. If you go to the police and claimed responsibility for a crime, the expectation is not that you'll be put on trial, but that you'll be sentenced (though in practice the Police might disbelieve you and make you leave). Likewise, Hirohito's assumption of responsibility ought not be considered an offer to stand trial, but rather a submission to Allied justice.
In some sense you could say he was making a guilty plea, though no formal charge had been laid against him. Trying to impose Western judicial systems on what was then a wholly different society was bound to be awkward like that.
Since the Allies had already decided against indicting the Japanese Emperor, his offer was rejected.
The meeting was described in MacArthur's memoirs. The relevant excerpt is:
I tried to make it as easy for him as I could, but I knew how deep and dreadful must be his agony of humiliation. I had an uneasy feeling he might plead his own cause against indictment as a war criminal ... But my fears were groundless.
What he said was this: "I come to you, General MacArthur, to offer myself to the judgment of the powers you represent as the one to bear sole responsibility for every political and military decision made and action taken by my people in the conduct of war."
A tremendous impression swept me. This courageous assumption of a responsibility implicit with death, a responsibility clearly belied by facts of which I was fully aware, moved me to the very marrow of my bones. He was an Emperor by inherent birth, but in that instant I knew I faced the First Gentleman of Japan in his own right.
- MacArthur, Douglas. Reminiscences. Annapolis: Naval Institute Press. 1964.
The offer was probably sincere, and certainly courageous - he could not have been sure the Americans would have rejected it. Yet its real purpose must have been to underline to the Americans that if he was to be spared immunity from prosecution - as his advisers had every reason to believe that he would be - the grounds for convicting his subordinates were flimsy indeed. As he had assumed responsibility, he must be prosecuted or pardoned, and his subordinates likewise. The Americans perhaps deliberately turned a blind eye to this gambit.
- Harvey, Robert. American Shogun: General MacArthur, Emperor Hirohito and the Drama of Modern Japan. Overlook Press, 2006.
I have no idea whether the offer is true or not, but it runs true to the Showa Emperor's beliefs. There is a fair amount of evidence that he was not a supporter of the militarist bent taken during the 30s and only accepted the war as a fait accompli. Japan entered the war of the 30s and 40s mainly due to fanatic junior officers taking the law in to their own hands in 'the name of the Emperor'. The Emperor himself sadly could not comment on the actions because 1) his voice was too holy to be heard (how convenient) and 2) during his stay at Buckingham Palace at a guest of George IV in 1921 he is said to have become a devotee of constitutional monarchy in the British style. i.e. he believed he could not interfere in the 'democratic' process. Interestingly, Japan was the only belligerent in WWII to not suspend elections, therefore preserving the appearance of democracy on the outside. This is a very plausible situation as the Japanese monarchy was very Anglophile at the time and Hirohito is quoted as saying his stay in Britain was the happiest time of his life.