Angels are one of the three main races of the Monster Girl Quest setting, the other two being the humans and monsters. They are a race of divine creatures led by Goddess Ilias, the manifestation of light.
The usual form of an angel resembles a human woman with feathered wings and a halo. However, there are many deviations from this. Some angels do not have halos (e.g. Valkyrie), and many of the higher-ranking angels bear monster-like traits (e.g. Archangel Ranael has tentacles for a left arm, a venus flytrap for a right arm, snakes for hair and scylla tentacles for feet).
The body of an angel is comprised of holy energy. This composition means that most attacks pass harmlessly through them; a major advantage in battle. The only things that can harm an angel are another angel or the sword Angel Halo, which is made from hundreds of angels. Angel Halo can erode their bodies until they eventually transform into a being of pure holy energy.
However, if an angel is a hybrid, i.e. part monster or human, they can be naturally harmed due to these mixed genes. For example, Promestein, a former full angel who gained monster traits due to experimentation, and Luka, an offspring of an angel and a human, can be injured by humans and monsters. Additionally, because Luka is half-human, his half-angel side endangers his life.
According to Torotoro's blog, the angels could be physically harmed at the time of the Great Monster Wars. However, no further explanation was given.
In the original Monster Girl Quest, surface dwellers were eventually capable of harming angels once the holy energy of the world was distorted using the Four Towers. In the world of Monster Girl Quest: Paradox, one of the effects of the Great Disaster was an increase in the holy energy in the surface world, also allowing surface dwellers to harm angels.
When angels are defeated by Angel Halo, their corporeal form is sealed, and they are reduced to their original holy state. Instead of being reduced to a sealed form, their bodies become particles of light and fade away, though this functions similarly to a monster or human being sealed. Once they accumulate enough power, they will regain their corporeal form. However, according to Torotoro's blog, the more powerful the angel the longer it takes for them to revive. For example, while Cupid and Valkyrie are revived shortly after they were defeated and Archangel Mariel returns one month later, Seraph Eden would take approximately a hundred years to return.
An angel's holy power can be fatal to humans exposed to it, causing their bodies to erode until they are transformed into a being of pure energy. It is unknown if this affects monsters, but unlikely due to holy power being naturally incompatible with their dark energies.
Angels are also known to have abnormally high regeneration. A fallen angel was said to have used Meditation in order to heal injuries, which Luka frequently applies in the present day. A more notable example is when Luka recovered from extremely severe injuries in just one night of rest when it was predicted it would take him nearly a month. Despite this, none of the angels in the game are ever seen using regenerative powers.
Like monsters, angels also gain energy from a human`s sperm, and can be impregnated. However, angels do not necessarily need this as an energy source.
Angels have the lowest population compared to other races. This is due to many reasons: Ilias having abandoned the creation and development of the angel race, the angels originally being forbidden to have direct contact with humans, the angel forces being inferior to the monsters during the Great Monster Wars, and the angel race being mostly exterminated by the "Angel Killer" Heinrich.
An angel's lifespan is said to be approximately 10,000 years, according to Torotoro's blog. However, characters such as Valkyrie and Principality Nagael intend to punish Luka for 20,000 and 100,000 years, respectively. It is possible that this limited lifespan only applies in situations such as the epilogue of the original Monster Girl Quest, where the holy energies on the earth have been weakened and Heaven has disappeared.
Despite being seen as "good and holy" figures, they are actually evil and destructive just like their goddess: the angels caused the Slaughter of Remina along with the Chimeras under their goddess’s command, and even fought against Heinrich 500 years prior. Although angels seem to have free will, a majority of them are extremely obedient to Ilias and thus blindly carry out all her commands; in actuality, Ilias shows no care for her own kind and views them as sacrificial and expendable pawns. When Luka revolted against Ilias, the angels began taking action and attacked the surface world to wipe out all humans and the lowly monsters who refused to follow Black Alice.
All angels except Ilias herself are classified by the Hierarchy of Angels into one of nine ranks or "circles". This determines the angels' strengths and their assigned duties on the world, though 90% of the entire angel race makes up the ninth and lowest rank.
Angels were born as offshoots of Ilias, who attempted to counter her loneliness. Eventually growing bored of creating angels, Ilias turned to create humans. However, Ilias was rivaled by Alice I, the manifestation of darkness itself, who created monsters at a much more faster and controlled rate using her dark genes, which Ilias grew jealous of. As a result, Ilias declared war against the monster races 1,000 years prior, creating an event known as the Great Monster Wars, with the angels fighting alongside Ilias. Although the angelic forces were inferior to the monsters, the two goddesses knew that their constant clashing would ultimately destroy their creations, but Ilias continued her onslaught despite risking the demise of the angels. Alice I then surrendered and sealed herself away, but warned Ilias that slaughtering her monsters would result in the seal breaking.
500 years ago, Ilias plotted to exterminate the monsters without risking the resurrection of Alice I. Ilias needed someone to control the darkness in the world: Black Alice, the eighth Monster Lord with intense hatred against humanity and an immense desire to rule the world, and Promestein, a "rebel" angel with vast technology (including artificial monsters in the form of chimeras. However, the seraph Lucifina deemed Ilias insane and left to become the first fallen angel, briefly resulting in a confrontation with the seraph and her elder sister Micaela before managing to escape. Lucifina then wandered the world for hundreds of years. Heinrich also turned against Ilias around this time, using the sword Angel Halo (which he received from Lucifina sometime before her rebellion) to slay and severely decrease the angel population, before dying from overexposure to their holy energy.
Thirty years ago, Ilias assigned her angels and Promestein's chimeras to assault the city of Remina, a coexisting place of humans and monsters, driving a wedge between the two races as well as exterminating those who refuse to follow Ilias. Ilias claimed Remina was performing large scale magical experiments (which was true, but this was merely an excuse), but Micaela knew the truth and, acknowledging Ilias's insanity, also became a fallen angel.
A few years before the present day, Lucifina eventually met and fell in love with the human Marcellus, giving birth to a human/angel hybrid named Luka. However, Lucifina eventually died from a plague after sealing off her powers via the Keepsake Ring. Luka inherited the ring and it also kept his angel powers in check. Micaela also settled on earth and monitored Enrika, a safe haven for monsters. In present day, Luka eventually grows old enough to venture out into the world, but is informed by Ilias to defeat the Monster Lord, who is actually his traveling companion Alice XVI.
Once Luka fails to bring himself to kill Alice, he realizes Ilias is the true instigator behind everything and turns against her. As a result, Ilias sends her angelic forces, coupled with Black Alice's rebel monsters and Promestein's chimeras, to assault the entire world and create a new one. However, Luka, in possession of Angel Halo, is the only one who can defeat the angel army; his hidden angel powers are also unsealed after his Keepsake Ring shatters out of anger against Archangel Ranael. Later, the Four Heavenly Knights distort the holy energy of the world in the Four Towers; with the humans and monsters unified and united by Luka, they all counterattack against Ilias's second wave of angel forces, who are surprised at their new vulnerability to attack.
Meanwhile, with Ilias left completely defenseless and unguarded by her angel followers, Black Alice and Promestein betray her, planning to become the ultimate entities of light and darkness by infusing themselves with the power of angels and monsters. Black Alice absorbs Ilias after injecting herself with the White Rabbit which contains Alice I's genes. Luka defeats both of them. However, Ilias emerges from Black Alice's remains and reveals her true master plan: to become the ultimate entity, incorporating the power of monsters and Alice I into her angelic body, even stating that the angel race was expendable to her. However, the human/angel Luka teams up with the monsters Alice XVI and the Four Heavenly Knights, and the angel Micaela, and takes down the evil goddess once and for all.
With Ilias out of the way, and Heaven vanishing following her disappearance, the world pushes forward to coexistence and forgives the angels, allowing them to live peacefully on earth. However, since most of the angels looked up to Ilias, they are unsure about what to do in this new world.
They kept the same characteristics as the original world, but because of the saturation of mana in the air, they can now be wounded by anyone strong enough to face them, although their power has nothing to envy to the more powerful yomas roaming the world.
Because of Ilias's death in the original timeline, the Great Disaster happened and Heavens got destroyed, forcing every single angel down on earth and forming the Snow Continent. With their goddess apparently disappearing, the angels turned toward Seraph Eden for guidance. This resulted in the creation of the small village of Snow Heaven, which is now managed by Archangel Ranael. They trade with the outside world by disguising themselves
As the continent remains unexplored, most people and monsters remain unwary of their presence. The only monsters aware are the shy local Polar Bear Girls sharing their continent, and both groups had come to accept each other.
Otherwise, a group of fallen angels has established residence in Enrika and partnered with the local monsters to create a small but thriving and united community.
As a whole, a lot of angels in this world are more accepting and less dogmatic in their dealings, likely a result of being forced to fend for themselves for thirty years. Some are still violently loyal to Ilias, but even they can be recruited by the Hero Luka on his quest to save the world.
Angels are guiding and overwatching every moved made by humanity under the guided benevolence of Ilias. While things seems good on the surface, they tend to get agressive quite fast toward those that do not act according to the plan of the goddess.
Zion, Gnosis and Eden are three seraphim coming from this world and going to the Paradox world with the intent to save as many people as possible by bringing the faithful to their own world. At the end of part 2, on Ilias's route, they talk with Luka, and say that while the number of people they can save is limited, it is better than let this world die, and they hope that they will be able to rely on his support.