I think I’ll pick this one up. Mainly because a) I doubt anyone else will, and b) it’s a good excuse for me to learn more about Japanese history, which I know next to nothing about.
So Oda Nobunaga’s brother, Oda Nobuyuki, was indeed a historical person who rebelled against Nobunaga. Katsuie joined the rebellion as well. I don’t think the historical Katsuie actually wanted to side with Nobunaga like his animated counterpart though.
Of course, the scene at the castle is not what actually happened. Nobuyuki lost the battle, and Nobunaga killed him. Katsuie was spared and later became Nobunaga’s faithful general.
The scene with Nobunaga showing up at her father’s funeral and throwing incense at the altar is historical. Nobunaga did indeed show up at his father’s funeral, dressed inappropriately, and threw incense at the altar. No one really knows why he did this. I think the lesson is supposed to be that he was a free thinker who wasn’t constrained by authority. Some monk is supposed to have remarked that one day he would lord it over entire provinces and no one could oppose him (although this is likely apocryphal).