The situation is different from the original work.
In the original work, Kiritsugu took the lead, investigating the participants in the Holy Grail War. Even if he knew about this, he probably wouldn't think much of it.
After all, Tokiomi was his enemy. What was there to think about?
Moreover, at that time, he was more focused on the priest, Kotomine Kirei.
Now, the leader has become Irisviel. As a true Master participating in the Holy Grail War, she would naturally be interested in the other participants.
So she had her employed tool person, Kiritsugu, investigate, and the result was discovering the recent activities of Tokiomi, one of the Three Founding Families.
Anyway, he was certainly going to participate in the Holy Grail War. Investigating his recent activities first was only normal.
Like what relics he had collected, what Servant he planned to summon.
To be honest, Irisviel was also troubled by her elder, Jubstacheit von Einzbern.
Alias, Acht.
Also the current head of the Einzbern Family.
Because he was excessively desperate for victory in the Holy Grail War, and since the Third War they had already stopped at no means, it was normal for him to hire the Magus Killer, Emiya Kiritsugu, this time.
Hiring outside help, right?
Last time, they hired outside help and cheated, got their account banned. This time, just hire a magus who can kill other Masters!
As long as they don't violate the rules by summoning a Servant, it should be fine, right?
If they get assassinated, what does that have to do with the Einzbern? That's the Magus Killer Emiya Kiritsugu's fault.
Anyway, the current situation is that the Einzbern Family is obsessed for victory.
Or rather, he's even more eager than Tokiomi to obtain the Third Magic and reach the Root.
No matter who obtains it, as long as it's someone from the Einzbern Family!
Initially, Acht wanted Kiritsugu to marry into the family and wed Irisviel, but who knew Irisviel would be born earlier than planned, and upon birth, she already possessed Command Spells, automatically becoming a participant in the Holy Grail War.
This ultimately led to Acht changing his plans.
Since they had already invited the person, just continue employing him as an assassin!
Later, Illya's birth also had nothing to do with Kiritsugu.
Due to Irisviel's situation, Acht still felt it wasn't safe, so he had Illya created as well.
Whether in the original work or now, it can only be said that Acht was obsessed for victory.
Fail this time, there's always next time!
Except this time, Irisviel wanted to experience the feeling of being a mother, so she had Illya implanted into her body and gave birth to her normally like a human.
Thanks to this, Illya can be considered the only direct blood relative in recent Einzbern history to grow from a normal infant.
It can also be said that the Einzbern started becoming deformed a long time ago.
Possessing powerful homunculus cloning technology, they ended up using it all on themselves.
For the sake of past glory, all direct descendants possess the genes of the Winter Saint, Justeaze Lizrich von Einzbern.
This is also why Irisviel looks so much like her.
Even the Einzbern participant in the Third Holy Grail War looked extremely similar to Irisviel.
…
Upon learning this news, Irisviel, as a mother, was naturally indignant. Plus, with the chat group, she naturally shared these things.
[Kaito]: I see. So your Three Founding Families have this kind of relationship.
Irisviel introduced the origin of the Holy Grail War and the Three Founding Families in the chat group. After she finished, other group members expressed difficulty understanding the mindset of magi.
[Irisviel]: Sigh, poor little girl. She's two years younger than my daughter.
[Sephie]: Irisviel, according to your birth date, you're only around ten years old, right?
[Irisviel]: Ahaha... I guess that's true, but I was born with an adult body! And I received a lot of knowledge!
Irisviel replied somewhat awkwardly.
The difference between her and others is that she was born, not given birth to.
So it's normal that she has only been alive for about ten years.
[Tearju]: I feel my family has a lot in common with yours. Unfortunately, your cloning technology involves areas beyond my knowledge.
[Irisviel]: Hehe, that's because it's enhanced by Magecraft.
In the field of biology, Tearju was naturally very curious, but unfortunately, she has no magical power and doesn't know Magecraft. Studying it would be useless.
However, she does have some insights on this topic. The successful case is, of course, her daughter, Eve.
She is a life form cloned and modified based on Tearju's genes.
But... she is also an out-and-out artificial weapon. Her entire body can transform into any shape, turning into weapons to attack. At the same time, her body is very strong, and ordinary attacks cannot damage Eve.
The attacks mentioned also Tearju's disastrous cooking. Eve can eat it with relish, and her body is fine.
[Kaito]: Speaking of which, is Tohsaka Tokiomi definitely going to give away his younger daughter?
[Irisviel]: Yes, I even saw a photo of the little girl. She's very cute too.
[Kaito]: Did you find out the specific time?
[Irisviel]: It seems to be a week from now. The Matou Family has agreed, but the adoption process takes time, like processing some documents with the Mage's Association, etc. Anyway, it's to make Tohsaka Sakura the heir of the Matou Family, so she can participate in the Holy Grail War as a Matou in the future.
[Irisviel]: Perhaps that's Tohsaka Tokiomi's intention. If he loses, his two daughters can still participate.
[Sephie]: That's quite possible. Still, I can't understand the mindset of you magi. I don't know if this will be a good thing or a curse for that girl, Sakura.
It seems it's not as simple as just sending her over like in the anime.
But this just right gives Kaito some time, so he doesn't have to rush over.
Let it be known, he's not interested in loli.
But that doesn't mean he won't save Tohsaka Sakura.
As the saying goes, if you go through Fate, you must participate in the 4th War. If you participate in the 4th War, you must save the poor Sakura.
She's only 5 now! At most, almost 6! So young and obedient, about to suffer that plot. Indeed, Matou Zouken deserves to die!
Therefore, Kaito wants to save her and also kill Matou Zouken.
As for whether to return her to Tohsaka Aoi in the future...
Ahem! That's a matter for later!