From Yen Press:
The “Roman Club,” a school group interested in the occult, to which he’s practically enslaved, has become boring for one Hideo Aiba. Until a girl named Kurumi Sahana shows up and wants to join up. But Sahana is no ordinary girl… When the two are left alone in the club classroom, Kurumi makes a special “request” of Hideo… From that moment on, Hideo’s dull life gets far more…frustrating.
Sundome literally means "stopping the moment before," and considering the content of the story, it refers to being stopped just before coming or ejaculating.
