I have some more opinions on the recent Mitsuhide letter and why he wanted to work with the disposed Ashikaga shogun Yoshiaki. Just before the Honnoji Rebellion, Mitsuhide was a man who has serious doubts on what course of action to take. Mitsuhide was probably a man with low self-confidence, a big mistake. If you want to be the supreme ruler of Japan, confidence is a must. While Mitsuhide was a decent Oda captain, he did not have the charisma or skills that Nobunaga had to be one man show. So in Mitsuhide's mind, he probably needed Yoshiaki (who still had the Ashikaga name and title) to rule through since he did not have the leadership he needed.
There is reasons why Nobunaga was successful. He had self-confidence, leadership, and charisma.
Nobunaga no tame!