Edifice of the Week: "typical" apartment building

This week's selection is not a famous landmark, nor does it tower over its neighborhood. It is simply a typical apartment building in Azabu-Juban. Of course, as we've reviewed in earlier posts, "typical" in this neighborhood can mean it is somehow different from the other buildings on the block.
























Why did the architect choose this shape? It seems an extreme choice to me--I mean, wouldn't it generate a lot more useful floor space in this ultra-crowded city to have this building "normally" squared off at the top? Wouldn't that bring in more rent revenues, or at least be more efficient?

Maybe there's another reason, a practical engineering concern that is beyond my comprehension. I know nothing of such things. But it may be that this is simply an example of our neighborhood's aesthetic: making something different simply for variety's sake.