Mitsuhide

Hideyoshi defeated Mitsuhide within a month, and was regarded as the rightful successor of Nobunaga by avenging the treachery of Mitsuhide.

Another possible motive is for revenge as Akechi Mitsuhide's mother (or perhaps aunt) was killed because Nobunaga had gone against a peace treaty to which he had previously agreed.

A variation of the concept states that Ieyasu was well aware of Mitsuhide's feelings regarding Nobunaga and simply chose to do nothing for his own benefit.

But they were too late, as Hideyoshi—on his own—defeated Akechi Mitsuhide at the Battle of Yamazaki ; the later died few days afterwards.

Hideyoshi secured his claim as the rightful successor of Nobunaga by defeating Akechi Mitsuhide within a month of Nobunaga's death.

Ieyasu managed the dangerous journey back to Mikawa, avoiding Mitsuhide's troops along the way, as they were trying to find and kill him.

Mitsuhide chose that time to attack.

Nobusumi married Akechi Mitsuhide's daughter, and was killed after the Honnō-ji coup by Nobunaga's third son, Nobutaka, who suspected him of being involved in the plot.

The situation was fueled through several public insults Nobunaga had directed at Mitsuhide that even drew the attention of some Western observers.

This accomplished Mitsuhide's goal, although Nobunaga betrayed the peace agreement and had Hideharu executed.