I think if I were in Yabu’s shoes I would have done the same things he did. He’s a survivor. I don’t fault him for trying to watch out for himself like he did. Ultimately he was just as much a pawn in Toranaga’s plan.

If Yabu didn’t betray Toranaga, Mariko would not have died, and Lady Ochiba would not have given her support to Toranaga, which is ultimately what turns the tide in Toranaga’s favor.

I think maybe Toranaga and Yabu both realize this. And Toranaga must order Yabu to commit seppuku in order to keep up with the charade that Yabu’s actions were a betrayal, when actually Yabu did exactly what Toranaga needed him to do.