Sōseki wrote this summer hokku:
The red sun
Sinks down into the sea;
The sun sinks into the sea every day, so what is different about this that makes it worthwhile and not just a commonplace? It is the combination of the redness (very yang) of the sun combined with the intensity (we see it in the exclamation point) of the heat (also yang). Both are unified by the flat horizon of the sea to give a very strong physical sensation, which is what we look for in hokku.
The heat of the day is already there as evening nears. But it is the largeness, the redness of the setting sun that brings out its magnitude; we not only feel the heat, we see it in the redness.
The setting is “the heat.”
The subject is “the red sun.”
The action is “sinks down into the sea.”
As I have said before, we can write countless hokku on countless subjects using the combination of setting, subject, and action.