The story is as the review said. Studentxteacher. The key thing is the teacher used to date the student's older sister 9 years ago. There was a break up and they were apart for 9 years. During that time, rather than her love faiding for the teacher, the student remains deeply in love with him. So when he becomes her teacher she still loves him.
Another thing to note is that it seems the teacher had a thing for the student even as a child, because he specifically remembers her and seems to alude to some sort of an
attraction. There happens to be an 11 year gap between them (I believe).
The story is average at best. It's not taboo or risque in the salacious sense, however the concept of a grown man having an attraction to a child and then years later maintaining that attraction when he met her while he was dating her older sister is extremely taboo. The rest of it is an average love story with good artwork.
It was a nice one shot.