@AncientWatcher @silentfx @Escheron
The signs on their houses show that they're neighbors (as Ancient mentioned) and remember that they're also childhood friends. In a lot of places, it's not "breaking in," because it's the whole "my house is your house" idea. Idk it's a normal thing for a lot of people and I'm surprised there was talk about it, so I hope that clears it up.
Also, he's not shocked in concept so much as surprised to see his magical world of them hanging together being broken, and annoyed that it was. Like he's not surprised at the logistics, if you see. I'm guessing that this is the first time he's had such an adverse reaction to her coming over, specifically
because this time he's with Shion.
As for the "But why's she here!" on page 16, I have to assume he's wondering why she's here
then, because generally there would be a reason why they'd go into each others houses; especially if their families are close, she might join them for a meal or something, but that's not happening here.