u/Emotional_Meet2467

Holy King (王聖, O-Sei)

>A King is not born in the human world, but is sent from Heaven. Kings born this way are said to possess the divine right to become the Holy King. A natural ruler, the pure, young king shines like the sun. The Holy King is the embodiment of an ideal.
Ideal Holy King, FGO CE

First appearing in Fate Extra, Holy King refers to those who are said to possess regality from the moment they are born, and have an otherworldly natural charisma that causes others to gravitate towards them. With their resolve, Holy Kings will give their best effort in re-stabilising the world, turning it into an ideal land where no evil and tragedy exist, a land in which each individual can find their value and become equal. However, the presence of a Holy King also announced that the world had gradually reached a dead end, and was preparing to welcome a new age. 

From what has been shown, Holy Kings have an extremely close relationship with the Representatives of Human Order, because an ideal world is one that is unable to progress. Thus, it needs someone to step up and carry the responsibility of leading people forward.

In another word, Holy Kings born and become one of the final obstacles for Representatives of Human Order. Only by shattering that absolutely ideal of euphoria, can humans open a new age for themselves. In this process, a Holy King will guide that chosen individual, and sometimes sacrifice their own life to ensure their safety or pave the path for them. 

Holy Kings - Representatives of Human Order couples that has been shown until now:
- Extra: Leonardo B. Harwey - Kishinami Hakuno
- FGO: Kirschtaria Wodime - Fujimaru Ritsuka

Azrael “Thirty Birds” grant him or his ally Immortality, Revelation, and Holy King. It doesn't have a direct effect on himself, but still has some secondary effect. After his death and became The First Hassan, he still guided his successors until their death.

Furthermore, Solomon has been hinted to be a Holy King, but hasn’t been confirmed yet. A certain, nameless person in the Daji era are also called as a Holy King, but we know nothing about this individual.

>!McDonell Trambelio Elrod (Lord of the Department of General Fundamentals) has an air of a Holy King, and in Mahoyo, Aoko is mentioned to be a Representative of Human Order, but we still see no interaction between them (Mahoyo 6 when?)!<

Note: Even has the same translation, Karl der Grobe “Holy King” is completely different from this type of Holy King. Karl is (聖王): a skill that give him advantages against demonic enemies and non-saint divinities.

Image source

In case you guys forgot, the average strength of humans during the Age of Gods was described in the Nasuverse like this:

• The shape of their soul had a decent to very high compatibility with the Divine Spirits. >!That's why Ishtar herself wondered if a random modern girl like Rin was actually a citizen of Uruk who crawled out of nowhere, just because she could become a vessel for a God.!<
• The color of their soul for over 80% of the population was golden—the highest tier on the soul ranking scale. And one golden soul contains an amount of magical energy equal to 7 Servants. In other words, feeding one ancient human to the Holy Grail to make a wish is faster than actually running a Holy Grail War.
• Their raw physical strength was insane just to endure the crushing atmospheric pressure filled with True Ether. To put it simply, if you threw a random modern human back then without any gear, Mystic Codes, or protective magecraft, not just their lungs but their entire body would pop like a bubble.
• They threw hands every single day, so both their combat techniques and experience were monstrous.
• They hunted Demonic Beasts for lunch, saved them for rations, and used their hides, etc., for gear. They literally held normal Hydra hunting competitions and handed out chef licenses to whoever could butcher it.
• Their genetic code at this time was still close to the >!Origin of Humanity,!< so their physical condition was extremely robust under all circumstances. Plus, their lifespan was incredibly long—a person could live from 100 to a few hundred years if they didn't die from being killed.
• Furthermore, Demi-Gods physically weren't that much stronger than the average human of that Age. >!One particular Demi-God had PTSD after throwing punch with a human, while another had to be very careful when battling a normal general. Both of them are strongest Greek heroes btw.!<
• Besides that, >!the Unified Language was still commonly used in several regions.!<

But by some True Magic, when it got adapted into an anime, it looked like this.