Incubus and porn star, porn stars who are also professor/student, soccer coach and kouhai. Not bad. :)
I really enjoyed the professor/student one. I like their relationship very much. The professor/student is the one where the student's AV partner (the professor) kept him as the only partner for videos. In the end, he finally figures out the professor really does bring his sexy side out and the student finally admits he loves the professor.
Koakuma wa Ore no Iinari