The universe Ruther lives in is, unless stated otherwise, very similar to the universe where we ordinary non-fictional beings live. One of the major differences is the explicit, very real presence of mana, a force that links all things, places and people, turning possibility into reality. The use of mana is called, you guessed it, magic. The other major difference is that there are no humans, the entire universe being populated by anthros and similar beings. 
In a distant corner of a certain galaxy, lies a world much like our own, which we will call Gaia for the sake of simplicity. It (and its other dimensional counterparts) is where most of the fun things happen, so we'll concentrate on it.

Gaia, the silver moon world
Gaia looks, in many important ways, very similar to Earth and can be assumed to be like Earth unless stated otherwise. The first big difference is that magic has created a number of extreme ecosystems compared to the ones on Earth, like impossibly thick forests with skyscraper-sized trees or glaciers made of diamond-hard ice.
Gaia is moderately rich on mana, and its use was discovered early. That led to industry developing around magical solutions alongside engineering and math. Computers exist but work quite differently, voice interface and personal AI evolving faster than things like GUIs or mice. There's no internet as we know it, but AIs can link with each other to provide an equivalent.
The chief difference in technology is that fossil fuel never really took off after coal, magical alternatives turning out cleaner and more effective. Heavy industry is much less prevalent. Airplanes are rare outside of military uses, with airships dominating the skies. Portals are the fast transportation of choice, linking two points in space (or across dimensions) instantaneously after being set up (anyone who's read Hyperion will be familiar with how those work).
In the wake of the demon invasion, there was a spike in military development among the formerly peaceful Gaians. After the war, disaffected soldiers and military hardware manufacturers have established several paramilitary organizations that have since become a major thorn in efforts to restore peace. Groups such as Black Bow, NIAKS and Spartan Spiders have reverse-engineered angelic magic and technology to become formidable enemies to angel and Gaian alike.
Gaia's moon is Selene, being very similar to our plain ol' moon except the rocks are actually silvery grey (as opposed to the very dark brown of the real moon) and that it's inhabited. An advanced civilization of saucer-and-monolith building psychic lizard people (known as Selenians) live in the dark side of the moon, along with a population of moon dragons.

Shamayim, the blue moon world
Shamayim is one of the alternate-dimension counterparts of Gaia. The planet itself has been almost entirely built upon, forests and mountain ranges replaced with gardens and buildings.
Shamayim's dimension is oversaturated with mana. That makes it the dimension of choice for creatures that normally depend on a lot of mana to thrive, like dragons. It also makes the universe much more populated with monsters in general. It's not a safe place to visit, despite the huge opportunities the increased amounts of mana bring.
The main inhabitants of the planet are angels who worship a machine-god they call Logos. The Logos has given them advanced technology and changed their form to be between mechanical and organic. Low-level angels are anthropomorphic animals which gain mechanical parts at the Logos' discretion when they come of age. The mid-ranking ones (Cherubim) look like mechanical versions of actual animals, sleek and covered in some kind of carbon fiber-like smooth material. The higher-ranking ones (Seraphim) are energy beings encased in suits of armor, whose brilliance alone can burn. The angels are actually a multiplanetary civilization, with only a small part of them assigned to Shamayim.
It's called the "blue moon" world because its moon, Sahar, has a blue tint. It's home to the magically advanced civilization of Crystal Eternity. They're not angels, but normal anthros who have lifespans of thousands of years and rarely, if ever, reproduce. In certain rare nights, Sahar can be seen from Gaia instead of Selene, it's when the dimensions are closest.

Irkalla, the red moon world
Irkalla is poor on mana, and thus the inhabitants use souls as catalysts for magic. Souls are pretty much infinite sources of mana if not overused, but they're also sentient, and the process is traumatic for the soul in question. Souls power the meager comforts of this world for the few who can acquire a bunch of them. Portals are a privilege rather than commonplace, the most treasured of all being the ones leading to Gaia, which allow demons to try and capture souls outside of their own realm. Necromancy is a favored branch of magic, as it uses the one thing that's plentiful in Irkalla - death - and turns it into an asset with little waste.
The war between Irkalla and Shamayim started ostensibly because the demons decided it wasn't fair for them to live in such a harsh and desolate universe when mana was so abundant in the neighboring dimensions; they wanted to conquer Gaia so it could be "mined" for easy mana. The demons suddenly showed the ability to open large numbers of gateways in an unprecedented scale. Gaians were initially overwhelmed by the demons' number, tenacity and necromantic magic, but the angels showed out to help, and responded with swift and disproportionate retribution.
However, it was later revealed that the reason Irkalla had invaded Gaia in the first place was because a cadre of runaway angels had joined the demonic hierarchy and forced a war to get revenge on their brethren, and the angels went into all-out mode to root them out. The big battle between heaven and hell, thus, ended with heaven's decisive victory and most of the traitors thrown into Shamash, Irkalla's soul-devouring sun. After managing to destroy the conspiracy, the angels  retreated and left demons back to their own devices.
Currently, Irkalla is living a cold civil war between the demons that still follows the angelic traitors, the ones that want to welcome the angelic host to rebuild, the ones who resent them, the ones who still believe they should acquire mana from the other dimensions by force, the ones who just want to move on and try to live in peace, and so on.
Sin, the red moon of Irkalla, can be seen in the place of Selene on the skies of Gaia during total eclipses. It's currently the base of operations of the last remaining dark angels, and populated by horrific flesh-eating monsters.