erm.. the title literally the plot in both ways..
MC Met ML after he was getting chased by researchers to give him his daily injection so that he doesn't turn into a beast. MC, however didn't like the fact the researchers were being scary to child ML so he stopped, calmed him down
then he became a groomer (animal kind) and took care of him everyday
one day, ML few into a teenager (like really fast) and had an erection and MC took care of that
later in the story, they both have sex
Grooming