A Herrscher? Though that sounds a bit improbable since it looks like Kotomine and Kiritsugu aren't S-rank valks who would have knowledge of that.
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Hmm, could just be something else that generates Houkai energy, though I'm not entirely sure what else can.
[X] One task will give Shirou time to settle in at St Freya before the start of the school year. He'll be able to meet with the people he'll spend his time with, get his bearings in what resources are available to him, and get a decent footing in the coursework, especially the parts he knows are going to be hard for him.
[X] Spend time at home with Taiga and Sakura, some quality time before he leaves. This will be the last time he'll get to see his family until the next school break, after all. He should enjoy it.
We'll meet Kiana again...maybe, prooobably. Should probably spend time with Sakura and Taiga before Shirou goes off to St. Freya.
Thinking on it, if PW is preserving roughly the context, then it's probably something to the effect of Irisviel turning into a pseudo-Herrscher. Or being turned into one, because Schicksal has no sense of right or wrong.
It would explain why Kiritsugu left the organisation on such bad terms.
Since we've started talking a bunch about Herrschers, may as well give a little infodump on them - Pale Wolf will probably talk about them in a St Freya class, but as a brief primer:
Herrschers are the human representatives of the Honkai. Due to a variety of reasons, a regular human - usually one who has been victimised by humanity to some degree - becomes infected by a vast amount of Honkai energy, more than a human should be able to take,
and they do not die.
instead, they are some of the most powerful and dangerous enemies humanity will ever face. Their creation/ascension is marked by a sudden spike of Honkai energy in their environment, killing any humans nearby and turning them into zombies, as Honkai Beasts appear around them.
The First Herrscher and the First Eruption occurred in the 1950s, Berlin. There's not a lot of information on this, but it's safe to assume that thousands died at a minimum. But in comparison to the Second, this was nothing.
The Second Herrscher Erupted in the early 2000s, in Siberia. Though the isolated origin meant that there were relatively few casualties intially, the Second Herrscher likely killed millions, directly and indirectly, as the Second Honkai War raged on. Given that the War lasted perhaps - a month at the outmost, likely closer to a week or so - a lot of people died, rapidly. The official story is that the S rank Valkyrie of the time, Cecilia Schiariac, Kiana's mother, fought the Herrscher in a stalemate, whilst Schicksal fired several Honkai fission missiles at their location to kill the Hersscher.
The Third Eruption has not yet occurred, but it is the inciting incident for HI3, which takes place a year or so after it. It occurs in Japan.