So it's not just SHOCKERS POV, this Manga further explores Hongo (and of course later Ichimonji) inner though. Man this manga is peak and a must read after you watch the movie.
Is it wrong to brainwash people if it's for justice?
I think in the past, I read some story where one of the villain think like brainwashing is justified if it's for good.
So Hongo didn't think of saving Ruriko. It was the Prana within him. And Kumo wanted to be killed. It was probably why he volunteered to meet with Hongo. He probably believe that he can be killed.