Julius B. Harwey

Julius Belkisk Harwey.
He is a Master, but not a Wizard.
He is a captain of the West Europe Plutocracy’s private army (Counter-Terrorism Unit) and is a skilled assassin who has worked in the shadows to eliminate many enemy forces.
Julius has a different mother from Leo, and participating in the Holy Grail War is part of his mission to support Leo. Julius was given the Servant Assassin who was summoned by another Wizard who used to be in Leo’s service.

As a child of the Harwey family Julius had high expectations placed on him, but it became clear while he was still in the womb that he was powerless and defective.
The Harwey family threw him away as garbage for the reason “this child will bear us no profit” but Julius managed to survive thanks to his abnormal willpower, and in time he crawled up the ladder to his current position.
When Julius turned six years old (coincidentally the same year that Leo was born), in order to be “profitable” for the family, his youth was essentially discarded, and his body was forced by various medicines to rapidly develop into an adult body.
Three years later his existence was finally deemed to have some value, and after completing his first job he was placed out of sight and out of mind in the Harwey assassin unit.
This is why he has so much combat experience despite being as young as he is.
He was able to gain enough sway over the other members of the unit through sheer willpower rather than relying on talent or his household’s authority.
If Leo is the light of the Harwey family, then Julius is the dark. Julius takes all the darkness upon himself and walks the villainous path.
This is once again digression; however Julius’s physical body that lies dormant on Earth is half dead.
Julius’s body has been modified so much that he will no longer be able to function normally as a human after this mission. He is organically connected to the Harwey super computer. Using the backup of the super computer to his advantage, Julius pushes the limits of the rules in order to eliminate all obstacles to Leo’s victory.

There is no future for Julius on Earth. He can never return alive.
Julius does everything in his power to make it so that Leo will win, but he doesn’t do this out of loyalty to the Harwey family.
When Julius was still a child Leo’s mother, Alicia, acted like a mother to Julius. Julius fights to protect and support Leo because of her words. “Take good care of Leo for me.”
The short time Julius spent with her was the only time he was able to be like a normal child.
However it ended all too soon.
Disdained as a defective product, he was given a harsh first test of his skill.
“Leo will be the next King. Eliminate everything that is unnecessary to him.” said his father whose face he had never seen.
It was a moonless night. He walked along the familiar path he often took to her room.
Beautiful long golden hair. A calm and peaceful sleeping face.
A small clicking noise resonated in the room as he started to pull the handgun’s trigger.
Her gentle voice replayed in his head.
“Take good care of Leo for me.”
Bang. The dull sound that came from the gun.
Julius lost the only person who had ever tried to cheer him up, and at the same time he finally proved his worth [to the Harwey family].

In the preliminaries Julius is the only Master who thinks that the protagonist might pose a risk.
Thanks to Julius’s keen sense, he was able to see that the biggest obstacle to Leo’s victory was in fact the protagonist rather than Rin or other favored Masters.
That naive amateur would prove to be a rock that the King would stumble on.
After a series of clashes, the protagonist encounters Julius in the 5th round.
Even after being defeated and dying, Julius remains as a vengeful ghost and once again faces off against the protagonist in the final layer.
The reason that Julius is so obsessed with the protagonist is not because the protagonist is Leo’s biggest obstacle, nor because Julius realized the protagonist’s true nature.
It’s simply because Julius is furiously irritated.
Just like Julius, the protagonist worked his way up from the bottom. So when they met the protagonist could immediately and clearly see through Julius, and this aggravated Julius to no end.
Julius would only find out the cause of his vengeful impulse in the final moments before his complete destruction.

Julius also appears as a Master in CCC.
Since the protagonist can’t remember anything, as far as he/she is concerned Julius is just a very slick handsome guy that always seems to be at Leo’s beck and call.
Julius is the Student Council’s secretary. He can be a bit gloomy, but he is a reliable young man.
Actually Julius has retained just one memory.
He remembers turning into a vengeful ghost and trying to attack the protagonist, and his resulting “complete destruction” (death). He didn’t die in the fifth round, and only died much later after becoming a ghost.
BB has no idea that Julius survived till much later than the fifth round as a ghost, and mistakenly pulls the “ghost” version of Julius back into the fray of battle despite Julius knowing everything that will happen until the seventh round.
After being employed as one of BB’s pawns Julius pretends to have died holding a grudge against the protagonist, but he actually takes action to support the protagonist from the shadows.
The reason he does this goes without saying.
In the last moment before being destroyed when he was ghost, Julius finally found the light he always desired.

Fate/EXTRA Material: Encyclopedia of Fate/EXTRA