The straight line dominates Japanese architecture to such a degree that whenever I see curves or any sign of ornamentation, I'm either immediately repulsed or intrigued.
At one of our local temples I experienced the latter with these kato mado ("flame head windows.") With their scalloped tops and rounded corners they feel more Persian than Japanese.
Indeed, the kato mado came to Japan from China at the end of the Heian period (794 - 1185) reportedly via monks who were escaping a war with the Mongols that toppled the Sung Dynasty. (I'm guessing the monks carried the design in their heads, rather than the actual windows in their hands.) How and when the design reached China itself, or if it was an indigenous creation there, I don't know.
But according to people who study this sort of thing, the really radical aspect of this type of window in Japan was that it overturned the very notion of the window's function. Whereas previously there had been no real distinction between window and door, the kato mado, being an opening in a solid wall, directly focused the viewer's attention either inward from the outside and outward from the inside.
With the introduction of Taoist thinking and practices that came with the monks and their windows, the halls in the temples became more of places for meditation than they had been previously.
I especially like this second example, from one of the temple's outbuildings, with its bowing latticework creating uneven lines: