Question

Hitherto she had steadily borne up against the pressure of her malady, and had not betaken herself finally to bed; but, on the closing in of the evening of my arrival at the house, she succumbed (as her brother told me at night with inexpressible agitation) to the prostrating power of the destroyer.
Which short story element does Poe develop in the excerpt?
characterization
plot
setting
theme