I am trying to ignore the "NTR" but author draws the dude and girl in such a pervy way, with all the looks the dude gives, and all the close behaviour of the girl around him, that its hard to do that.
As a side not as a leg-guy - half the time girl has her legs drawn beautifully, half the time she looks like she has anorexia on her thighs and was a heavy leg kinds athlete on the calves XD.