Ranmaru is a parody, that's the whole point of the show, not gods vs humans; if anything it's just momiji vs ichiko, which essentially boils down to "god of misfortune" vs "god of fortune"; polar opposites.
If you thought this was "god vs humans", then you've missed the fucking point.
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Did you seriously not catch any of the lines by either Ichiko or one of the dieties, questioning whether Ranmaru was really human? It only happened about a dozen times.
Not to mention the times that Momiji gets insulted for using disgustingly mundane ways to try and extract Ichiko's fortune, down to even the level of stuff like, "Hey, look a UFO!" ...[attempts to stab with syringe]. Or the gags where the gods (much like Nyaruko) have equally vain and average interests and get distracted by all sorts of stuff (Yamabuki having a thing for goth visual kei bands, playing off her disheveled bride outfit, a fairly common costume for fans of those bands).
Like DS said, it has never been about Gods vs Humans (particularly when a number of them betrayed Momiji for Ichiko). It's only ever been about Momiji versus Ichiko.
...and Momiji doesn't even really care about performing her task, they showed quite blatantly she is willing to undermine herself so she can continue to torment Ichiko in regular ways.
I think she cares about it a great deal, but just not the way her superiors would prefer. Throughout the show she has been teaching Ichiko the value of others and the few times she got a chance to extract fortune out of her, she made sure Ichiko understood how that fortune in turn helped people around her. Like her clean self said, she wanted to do the job, but not by ruining Ichiko. Even though her dirty self's methods are... dirty, in the end they have only benefitted Ichiko in the bigger picture.