The general setting of SSSS is that of the remains of humanity struggling to keep alive in a post-apocalyptic world. Unsurprisingly, the majority of named characters of the story are human.
Gods, cats, and monsters can be suspected to become major players later on, but so far, none of them have shown the kind of intelligence required to be more than coincidental individual major influences on the goings-on.
The human population has drastically diminished following the outbreak of the Rash Illness; in most parts of the world, it seems to have effectively dropped to zero, and even the most fortunate area of all, Iceland, has lost about one third of its pre-Rash population.
A large part of the technology that mankind possessed pre-Rash has become impractical, or even downright forgotten. It seems that a notable part of the survivors even suspect parts of the old technology to be to blame for the apocalyptic events, and preferred to resuscitate their beliefs in the old Nordic deities.
Whether it is related to these rejuvenated religious activities or not, one very noteworthy difference between typical pre- and post-Rash humans is the existence, and practical relevance, of magic. Used in sync with suitable - read: military and medical - technology, humans are slowly making progress in fighting back monsters and Rash alike and adding the cleansed locations to the safe areas they live in.