It was a snowy day as a homunculus was helping Irisviel deliver two babies. After an hour of pushing the first born, a boy with white hair as the mother kept pushing which made the second one come out, a baby girl with white hair started crying.

Irisviel: Kiritsugu, they are so adorable...

Kiritsugu: What do you suggest that you call them?

Irisviel: I think that the girls should be named Ilyasviel... as for the boy... I want you to name him, he is different after all.

Kiritsugu: Different?

The head of the Einzbern, took the baby boy as the homunculus gave him the child. Before dropping the child into a tube full of blood before taking him out as the boy cries.

Kiritsugu: WHAT ARE YOU DOING?!?! YOU ALMOST KILLED HIM!!

Head: You see, Kiritsugu, if we want to win the war, then we have to get our own trump card. Do you know who's blood is this?

Kiritsugu: No, I don't.

Head: This blood is the blood of the evil dragon. Fafnir. It was hard to get a full tube but with this, he'll become the reincarnation of the hero, Siegfried. One third human for survival, one third homunculus for incredible magic, and finally, ⅓ dragon for incredible combat. From this day onwards, he'll be the reincarnation of Siegfried!

The head then pulls out the baby and dries him off.

Kiritsugu: He will be named, Y/N, and I will be the one raising him.

Head: Do what you want with him, but I do need to fulfil my promise in the future. Now, I will take my leave.

Irisviel: Sorry about my father.

Kiritsugu: It's fine, Y/N is alright now.

Time skip to 5 years

Y/N was playing tag around the huge castle, perfect for playing as Kiritsugu runs after him.

You: You're too slow! Come dad, you have to do better than that!

Kiritsugu: Y/N, come here, it's time for your studies!

You: I don't want to study history! It's so boring to read heroes all day!

Kiritsugu: Y/N, I understand but you should know that this is for your own good! Now come here and stop this nonsense!

Y/N then soon gives up before crashing into the kitchen counter, which caused a knife to fly off and hit his stomach, but it bounced off.

Kiritsugu: I have to say, what they did to you makes parenting much easier since we don't have to worry about you getting hurt. Today, we'll learn about the oldest hero ever, Gilgamesh.

Kiritsugu and Y/N then go to the library as they start to study as Irisviel and Ilya bring snacks for them.

Ilya: Hey, Onii-Chan, what are you reading about now?

You: Gilgamesh, he was really prideful.

Ilya: Hey, want to go searching for chestnut blossoms? Please daddy, can we go?!

Kiritsugu: Sure, I think that Y/N has studied enough.

You: (It hasn't been an hour, yes!!)

Time skip another 2 years later

It was two weeks before the Holy Grail War begins and Y/N was looking in the mirror. He gets a feeling that the next few days that he'll be away are going to be bad. He and Kiritsugu are meeting with the Tohsaka Family to make their family stronger. When they arrived, they saw a man in a red suit walking with a girl with purple hair and eyes to a seperate car.

She and Y/N looked at each other as she looks away in tears as she gets in the car with the man while Y/N was confused. Y/N and Kiritsugu then meets the Tohsaka Family.

Kiritsugu: You called?

Mr Tohsaka: Kiritsugu, Y/N, we've been waiting for you for your arrival.

Mrs Tohsaka: Welcome.

Y/N greeted them as a little girl who was with them as they both scratched their heads and tilted them to the right.

Mr Tohsaka: It's nice to know that you and my daughter, Rin are getting along already.

You: Hey.

Rin: Hi.

Kiritsugu: So, let's get down to business. You know that both us are participating in the Holy Grail War so let's cut to the chase. This isn't about us. This one is for the next. In 60 years, the grail will appear and I have a plan on how all 3 families may win the war. Now, I know that only one may win the war, but Y/N is part of the Emiya and Von Einzben family meaning once he's old enough, he'll get the family crests. Rin here is my only daughter and like your son, he'll get our family crest too. Well, if you're unsure, Kiritsugu, Y/N can stay here overnight to get to know Rin better and you can fetch him tomorrow morning.

Kiritsugu: What do you think, Y/N?

You: I'll be fine

Mrs Tohsaka: Perfect! Rin why don't you take him to your room?

Rin: He's sleeping in my room!??!

Mr and Mrs Tohsaka: Yes.

You: (To Kiritsugu) I see where this is going.

Kiritsugu: Me too.

Mr Tohsaka: Have fun you two (Those 2 will make a great couple)

Kiritsugu: ...

Rin: Come on Y/N.

Rin takes Y/N's hand as they both enter Rin's room.

You: Wow, your room is really red.

Rin: What about it?!

You: Relax, I love red!

Rin looks away and pouts before Y/N calls her cute.

You: Rin, who was that girl that your dad was with a while ago?

Rin: That was my sister, Sakura, she was given to the Matou family.

You: I need to talk to your dad now, excuse me, I don't need help, don't worry.

When Y/N went to Mr Tohsaka's office, he wasn't too happy to see him even though they just met.

You: How could you break off a family by giving away your own daughter?!?

Mr Tohsaka: I was being a father, I can only show one of them my magic, so I gave Sakura to the Matou family in order for her to live and to become a powerful mage.

You: You're nothing but heartless, I bet it was so easy for you to say yes! A true dad wouldn't just give away his own daughter like some dog! You didn't show Sakura any love at all! The Matou family isn't so nice to people who are under them! *sigh*

Mr Tohsaka: It was either kill her or give her away

You:Listen, here's the deal, I will give my love to Rin but not because you say so, but because she deserves someone better to marry her and love her too.

(Shirou Emiya will remember that.)

Rin: How did it go?

You: Peachy. Look, I need to go somewhere for a while to catch some air, think you're okay with staying here?

Rin: Of course.

You: Thanks.

Y/N then takes out a sword from a small portal that he made as he ties it around his waist.

Rin: Cool! You can do magic?!

You: Yessir! Pocket dimensions, I can store anything and it'll stay there. I'll be back in an hour, toodles!

Y/N jumps out of the room through the window as he runs on the rooftops of every house until he reaches the Matou house. He enters through the window.

You: THROUGH THE WINDOW!! THROUGH THE WALL!! Okay that was fun, now to find the old grandpa dude or whatever.

Y/N then spots Sakura again, this time, with the head of the Matou family, he was dragging her somewhere, and he was old, very very old.

You: You won't go anywhere, cunt.

Old man: A servant?! What is one doing here?!

You: In the name of my master, I'm here to warn you (places bind spell) the spell I planted was a binding spell, I will know and feel if Sakura is close to those bugs. If she is, I'll kill you.

Old Man: Tch, fine, as you wish, I won't harm the girl.

You: Good choice.

Y/N then leaves as he jumps out of the window again and turns back to normal as he runs back to Rin's house before landing on her bed.

You: I have arrived!

Rin: How did it go?

You: She's fine

Rin: Thank you, Y/N!

Rin hugs Y/N as he blushes

Rin: Thank you... Hey, Y/N, since you're going to fight in the war, I need two favours from you. (Touches seal) Don't let my dad die and most importantly, you, don't die! If you do, I'll come after you myself!

You: Ok, I promise that I won't die, I'll fight and survive, for you, Rin

Time skip

Irisviel: It's time to summon him.

Kiritsugu: It is.

[There should be a GIF or video here. Update the app now to see it.]

As the ritual ended, the 3 were looking at a beautiful blonde woman as she looks at Kiritsugu.

Saber: Are you worthy to be my master?