Just to make sure it's noted: "Location of my choosing" will certainly be "right here, right now". So we should be ready for that.
Okay, I've been thinking longer about this and... I honestly disagree. For one thing, two of Yuki's friends are here and the sudden blaring
WITCH! WITCH! she has every reason to expect from fighting us wouldn't go over well. Not unless the place's magic is set up to regularly attract witches.
But there's another matter and it ties back into what Yuki said:
"This building is mine," Yuki says simply. "This city is mine."
Something to consider is that the Fukushima group appear to go through grief seeds like nobody's business. They took 20 seeds in a single day for a single fight, if a bad one, prisoner services for a single individual would have them going through five a week, and they're
notable for being quite expensive as a general rule.
There's been plenty of discussion as to what the Fukushima group could be spending so much
on, but one of the things is enchantment. The building looks like it's heavily enchanted, but by the same token, enchantment is something you
figure out. Even if this is her home, Yuki would have to figure out how to make her effects work, presumably using other buildings to do that. If her enchantments last long enough or are nigh-permanent she could have a pretty significant chunk of the
city covered with more rudimentary versions of what she has here.
Even with the likelihood that this is closely tied to Yuki's wish magic, it's unlikely to be limited to this building alone: I can't see a high likelihood of her having some special attachment to this place. This is an ordinary abandoned office building, not a place of emotional attachments. Or at least it doesn't appear special in a way that would apply before she made her wish and came to live here.
So there's both
motive to take the fight elsewhere, and likely capacity as well.
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In other news... I think I have perfect music for this spar: She's sparring against an incredibly powerful meguca in a home invasion scenario, wherein "home" appears to comprise "the entire city," so what better accompaniment then a pair of tracks named "Castle Doctrine" made for a videogame final boss?