According to Wikipedia (warning: spoiler everywhere), the first arc of this season is Past Arc. The one that tells the beginning of Rikuo’s grandfather – Nurarihyon. Sure seems like there’re some kind of relation between Keikain and Nura. I’m avoiding spoilers so I don’t know what is this exactly. Anyway, seems like there is some kind of difference between some clan members between past and current time. Could it be because their powers have been limited to certain extent? The personality, especially Yuki-Onna which I noticed most difference. Or could her be the grandchild of first generation’s Yuki-Onna (whatever that means)?