Nephilim are descendants of angels. more specifically half angel and half human. There has been cases of nephilims being born through blood transfusions. They are naturally strong, charismatic, attractive, intelligent, fearless natural leaders that also tend to be arrogant and entitled. Nephilim tend to be the "supernatural police", keeping the balance between humans and other creatures. They will tend to be good and "pure" because of their angel blood, but that doesn't mean that there hasn't nor won't be any evil nephilim.

Identifiers: Nephilim look and act human, but there are identifiers that can potentially reveal their true natures

1) Green, gold, violet, or gray eyes

2) Brown hair with a reddish/goldish tint in the sun, fiery red hair with strands of gold, or any shade of blonde

3) Slightly pointed ears

4) They're adopted or one parent is "dead/missing" (typically the father)

5) Taller than the average human

6) Can sense/see what humans can't

Abilities/Powers: They have superhuman strength, speed, intelligence/perception, combat, agility, and endurance. They possess omnilingualism (the ability to understand/learn other languages quickly), precognition (ability to see potential futures), clairvoyance (ability to gain information about an object, person, location, or physical event through extrasensory perception), healing factor, element manipulation, and in some cases, flight. All nephilim possess sacred blood, which can heal others with no drawbacks through transfusion (though depending on the dosage it may turn the human receiving it into a nephilim), be used to bless weapons (many nephilim weapons are even made with their own blood so that the weapon and nephilim are bonded and share abilities), and can be very dangerous to vampires. They also possess the power called angelic wrath, which the nephilim, when feeling an incredible amount of rage or despair, will start glowing and become twenty times stronger and more powerful than before (though this does come with drawbacks).

Weaknesses: Since nephilim are technically mortals, they are able to be killed like any other human, leaving them equally vulnerable to magic and being hunted by practically all species. One species in particular are angels, as they despise the nephilim and will only help them if they are ordered to by a higher power (Nephilim are also immune to miracles or angelic healing). Another weakness is angelic wrath, in which a nephilim will go nuclear as a result from extreme anger and despair (this can potentially kill the nephilim if they do not control it, and since it will leave them physically and emotionally exhausted to the point of a blackout, this leaves them vulnerable to the enemy). Their scent is very noticeable, especially to angels and demons as it repulses them and makes it easier for them to track them down.

Societal/Political Stuffs: Most nephilim lay low in human society and only answer to the Stygian Court, a court led by two blinded angels that were one of the first to come to earth to breed with mortal women. 

Mating: They are like humans, so their ability to procreate after reaching puberty is practically the same and do not care what gender or species their mate or significant other is.

Offspring: Offspring will inherently be nephilim no matter the gender or how potentially diluted the family bloodline is.

Life Span: The typical life span for a nephilim is hard to pinpoint, as many are killed before they reach a natural age. However, it is assumed that their lifespan is similar to a human's.

Natural Enemies: Every creature on earth, heaven, and hell.

Other: There are many different nephilim organizations, but one of the most reputable are the Stygian Shikari, established by the Stygian Court and is the main policers of the supernatural world