10 years ago...
When the whole Fuyuki City is engulf in liquid fire. Just then, a shallow void appeared along the flames.
On the other side, an old bald man entered the basement and found the white-haired man lying on the ground bleeding covered all his dead body of crestworms.
"That's what you deserved, Kariya. You are not worthy for the grail. You useless trash."
Then, the purple haired young girl approaches. Her face is pale but shows no signs of weakness and lack of emotion.
"Grandpa, that man. He tried to kill me?"
She ask the old man.
"Because he hates you, Sakura. He deserved it."
"That man, he's with Mom.?"
"Everyone hates you. Only me who cares."
"Father hates me. He loves Onee-san. He gave me to someone. They gave me away. They want to get rid of me."
After minutes ago, The old man went out of the basement and found the broken chalice. The black smoke vaporated from the chalice.
"Did you seek for a vessel?"
The smoke responded to the old man and entered the basement.
"Right my precious grail come within my masterpiece."
Days later...
Kiritsugu Emiya after war subsided with a huge casualties that caused the previous town of Fuyuki, he found himself happiness and redemption by adopting a kid that survived that night.
After taking the boy to the hospital, Kiritsugu then adopt the orphan child. He regrets everything he had done. Swayed by the loss of his wife and then, her daughter.
After the events on the Fourth Grail War, Kiritsugu's Image became popular to all Mages. After knowing Kiritsugu's intention, House of Einzbern put a barrier on the Mansion. It was to secure them from notorious Mage-killer that could destroy their plan.
Kiritsugu knows that if he couldn't take his daughter there, it will be too late for him. The girl will be the 5th Grail.
Knowing this, Kiritsugu cannot afford to lose her child. By that day, Kiritsugu came to Einzbern to take her child. However, when he came to the place where the Mansion is, he found nothing. The whole Mansion were sealed along with his daughter. He done everything he could but still couldn't break the seal. It was true that he is a Mage, but it is only by blood. He wasn't taught magic since he was a kid. The only magic he knew was Anti-Magic Sorcery. The only spell that a Mage Assassins could use to penetrate Spell Barriers, and Strengthening Magic.
With the spell he learned, he could somehow be able to unseal spells however, the Spell is so strong that only Mages with high Caliber could unseal it.
It's hard to accept that he could no longer save his child. He feel depressed and worry. Upon taking a long trip, he returned to Fuyuki. As he arrived, the sad memories came to swallow him. Standing on the isolated town, he recalled the moments when he blamed himself.
On the hospital nearby, he visits the injured boy that he saved that night. And that same day, he adopt the child.
He took all his earnings while on his mercenary job from the bank to build a house and lot for them.
It was hard for him to forget all those days. But upon looking the boy, he felt relief. He began to be a father to the boy and gave him so much attention. But, as the day passes, he felt aging. His body is weakening and the pain he felt almost everyday.
5 years later, as Kiritsugu live comfortably in peace. He doesn't expect to return on his old business as he found another threat appeared on the mist.
He knew everything about the man. About it's cruelty and madness of a mage. It's involvement on the grail wars, and one being the most terrifying mage in centuries that devise the Grail system.
At his current state, Kiritsugu is in his prime. He cannot move swiftly than before, and have a will to fight as he did overthrow all his goals and previous affiliation being a mage-killer.
Simply, he just wanted to stay out of there as possible. But the matter is, he cannot just let it pass without knowing the move of a certain magus. He secretly investigated the old man in the shadows.
Way back then, Kiritsugu was Master standing for A house of European Homunculus Mage that seeks to won the Grail, where he sworn his allegiance. But at the same time, works there as a spy.
Einzbern won the previous 3rd Grail War and attempting to win the next though. Just then they come out with an idea to preserve the grail. They planted the Grail into humunculus body.
To be able to retain the grail, they come out to the idea of multiplying it by reproduction. The plan involves mating of the vessel to human.
Kiritsugu has sought to end the Grail War. For he viewed that the War is the greatest threat to the world that could bring destruction. To put an end to it, he must join and win the Grail.
Einzbern seeks a potential mage to mate with their homunculus vessel. In order to join the Grail, Kiritsugu needs to have a mage with a family reputation (that's where Kiritsugu lacks on). He found Einzbern seeking a potential Magus to join their family, that's why he joined them.
In initiation, he must wed their princess and have a child with her in order for him to officially part of the family. Kiritsugu took it as a mission to achieve his goal, setting aside his feelings to the princess.
Not for long, the princess discovered Kiritsugu's plan of ending the Grail war and she agreed to help him. Unbeknownst to her, Kiritsugu plans to kill all the Mages participating the Grail War. For her love to Kiritsugu, even though Kiritsugu plans only to use her for the world's salvation, she's willing to sacrifice herself.
5 years before the Grail War happens, Princess Irishveil gave birth to their daughter Illya. Kiritsugu gave all the love to her daughter that makes Irishveil satisfied. Just then Kiritsugu discovered the truth about the Einzbern being a homunculus Mages and he was being used.
Kiritsugu doesn't want her daughter to be sacrifice for the Grail war. That's why he wanted to do anything he could to win.
Iri shares the same feeling as Kiritsugu. Even though, she ended up to be sacrifice. For her daughter's sake, she accepts the cost. Kiritsugu knows it all of a sudden. That makes his heart beats for Iri.
Even though Kiritsugu doesn't show affection, he deeply cares to his wife. But, he cannot do anything to change her fate. She must die to save the World and their daughter.
Before the conclusion of the War, Iri has been abducted and Maiya was murdered. He left alone again.
Kiritsugu chased after Iri but he's so late.
After the final battle, he's the one remains standing. Just then, the Grail sets up an illusion for him. There, he found her wife who just gave birth to their daughter. Afterwards, he was sent into another dimension he see her wife standing before him waiting for him to come.
Later on, Kiritsugu realized that everything is an illusion. And the Grail was planning to suck him in. He managed to get out of the illusion and found out that the Grail was corrupted by an unknown Servant.
By his remaining command spell, he ordered Saber to destroy the Grail. For he thought that it was the only option to kill the unknown servant and save the world from calamity.
However, after the Grail has been destroyed, the Calamity he feared to happen has occurred. Succumbing the whole town of Fuyuki in flames.
By destroying it, the Grail discarded Kiritsugu as a champion and revived Kirei Kotomine and give the title.
During the Calamity, Kiritsugu was left shocked and at a loss. Everything he sought shattered around him. On his desperation, he look anywhere searching someone that could still be alive. That's when he found the boy named Shirou.
But now that he found that man again, he feared that the tragedy will soon to happen.