Totsuka was his rock and Homra's ray of sunshine. His sword started crumbling the night that Totsuka died and he knew he didn't have much time left so he wanted revenge before he died.
So why in the hell is he all smiles and buddy buddy with Munakata in official art? I know its fanservice and all, but it just ticks me off a bit when he is like that. I prefer official art with Mikoto with his gang and/or Izumo and Totsuka.
Also it may be my bias for MikoTotsu, but with how much he cares for him its shocking there is like a couple pieces of official art of these two alone. Mikoto feels ooc to me when him and Munakata are alone in official images. Why are you so happy?