Rabou is an anime-exclusive character in Noragami, appearing in the last few episodes of the first season. He is a God of Calamity who fought alongside Yato and wishes to return him to his former self, although by the end, it was revealed that he was only attempting to do this so he could get killed by him. He serves as one of the two main antagonists of the first season, along with Nora.
Rabou is quite tall, with long silver/grey hair a single bright yellow eye similar to a hawks, he lacks a left eye. He wears baggy clothing and carries a sword on his back. His clothing is that of a warrior. He also wears a sun visor over his left eye socket. The insignia on it is similar to that of Nora's masks.
Rabou appears to be a cautious and careful character. He carefully gauges an enemy's strength and abilities before he will personally engage in combat. He enjoys letting himself get seen very briefly, as to hint to his presence and put his target on edge. He is also a cold character, killing humans, phantoms and gods alike (regardless of whether it's a paid job or a personal grudge). Deep down, however, Rabou is fully aware that his ways have reached a dead end but, unlike Yato, does not know how to change them. He believes that people will always hate and forget Gods of Calamity and so he wished to be slain by someone who truly knew him, namely Yato.
Ultimately, Rabou is a foil/evil counterpart to Yato- both are sword-wielding gods of war who killed many people in their past and have a history with Nora, but while Yato was able to move on in order to do honest work, Rabou stayed a killer and is unable to understand Yato's attempts to move on. To put in simplest terms, Rabou is obsessed with the past, while Yato is focused on the future, and even calls out Rabou for constantly bringing up times that don't mean anything anymore. Essentially, Rabou is what Yato would become had he been unable to change his ways and leave his past behind.