@DrFrost
Spoilers:
Kurumi's death is alluded to throughout the story. The hints are subtle at first, Kurumi's nosebleeds seem innocuous and although she gets sick every so often, she recovers completely. As the story progresses, however, the story adopts a darker tone. Through numerous panels, it is suggested that Kurumi prostitutes herself to a doctor so that she can afford medical treatment. In a slow curtain reveal, the reader discovers that Kurumi is dying, and she had known so from the beginning of the story. The S&M relationship between Hideo and Kurumi is tied closely with death. Kurumi's cold, distant demeanor isn't necessarily a sexual kink, but a coping mechanism for her inevitable end. She will never have sex with Hideo for she must never love Hideo; she does not have the time left to do so.
In this sense, Sundome, to stop the moment before, assumes two contexts. One concerning the sexual connotation where Kurumi consistently teases Hideo until he is on the verge of climax. And the other, concerning the framework of their relationship. The intimacy between Hideo and Kurumi deepens as the story progresses, but no matter how close they may get, how deeply they may feel for the other, nothing can transpire from it; they may experience everything a relationship entails except for the relationship itself.
To chase and to be chased, that is the tragedy of Sundome.