Well, no doubts about why Rina is treated like a child with that attitude of hers... xD
I always miss something less in stories by this author... but I just don't know what. Perhaps the narrative, somehow all his stories seem to be in a hurry to reach the hot scenes and this spoil the whole background (which otherwise can sense deeper than that then is used) and the possible evolution of the characters.
Or it may just be expecting too much of porn, you might as well be. xD