That cottage has an interesting design. The side walls are logs, while the end walls are planks. A traditional log cabin construction is self-supporting, but that's not as easily the case for something like in this chapter. In fact, I'm not sure I've ever seen something like that in real life. Technically the ends could be planed logs, but that doesn't really make any difference since whatever the case, they aren't interlocking with side walls. One can only assume the side wall logs have vertical holes drilled in them for dowels, making the side wall a single giant piece, basically, and then the end walls are anchored to that piece one way or another. Of course the log wall would have a vertical groove carved into it, to allow the end wall to seal the corner. Yet there must also be a structural solution to attach each log individually to the end wall, lest the log wall is potentially wobbly.
I'm sure the mangaka thought this all out.
Edit: Actually, if the end wall is planed logs, the vertical groove (of the side wall) and the matching end of the end wall could be shaped such that they can't be detached. A lot of work, for sure, but I'm sure magic and magic tools would help.