Episode 4 of Nurarihyon is pretty much straight action all the way through. Kana and Yura are right where we left them, being menaced by the Kyuuso Clan of rat demons. Yura kicked some rat tail with her shikigami, but when Kana was threatened she let her guard down and the two of them are captured. This turns out to be yet another plan to get Rikuo to resign as heir to the Nura Clan - Kyuuso lures him to their hideout and threatens to kill the girls at dawn unless he issues an official letter stating his resignation to the heads of all the clans. Rikuo, naturally, seems only too willing to resign - since he professes to want out of the arrangement anyway - but he's entirely too trusting of Kyuuso's promise to release the girls if he complies. His grandfather gets Rikuo's dander up, however, and his fighting spirit calls forth Night Rikuo and our first real extended fight of the series, with the "Night March of a Hundred Demons" with Rikuo at their head.
Along the way, we get a nice dose of demon politics - the rat clan has apparently deposed the Bakaneko Cat Clan from their territory. We get a fair amount of action and some nice GAR moments from Night Rikuo. On the whole, though, the episode felt kind of empty to me. None of the conflict swept me up as much as the character stuff from the first three episodes. The villain was pretty much cookie-cutter and the action scenes were modest. One problem I'm having is the obvious dichotomy between the two Rikuos. Not only are they completely different in personality and outlook, but unlike in, say, DN Angel they never communicate with each other - they're like two different people sharing the same body. In Tetsuwan Birdy that was fun - the interplay in each others heads was one of the best parts of the series. But here there's no connection, no commonality - and it lessens the impact of their situation. I'd like to see some elements of his demon self manifest in Day Rikuo, or some sense of communication between the two halves of his being - I think that would add a lot of depth and complexity to the core drama of the series.