Both were Kei roadsters built by major Japanese automakers with tiny form factors and even tinier engines. And while their production runs didn't overlap, they straddled the turn of the millennium close enough that they bred close comparison.
Neither are still in production at this point, but that could be about to change. Honda is presenting the S660 concept at the Tokyo Motor Show next month, and the latest reports indicate that Daihatsu is planning a Copen revival of its own. The company has, after all, showcased a couple of concepts hinting at the prospect over the past few years since the Copen's cancellation.
Whether the new Copen would strictly comply with Kei car regulations that limit both size and engine capacity, or grow beyond that class remains to be seen. As does the question of its export, but considering Daihatsu is more or less a division of Toyota these days, we could see room in the Scion lineup for a baby FR-S. Couldn't you?