The story;
Rebecca from Tentacular, is enhanced Human working for a corporation that deals with genetic enhancements and taking the human evolution to next level and has been succesful, they experiment it on sick people/disabled people and were who miraculously able to be cured but with one downside, their body and hormones could not handle it and they died, either with heart failure or something else, until our boy, Damon, who was the only one who was able to handle the "genetic enhancement"/ "Serum" that was administered to him (probably because he had complications when he was born), it has been hinted that it was Clair who bonded with Damon while administrating said "serum/Genetic enhancement" and he didnt have complication with it like other subjects. We find out that is the reason, he was horny and tittyfucked Claire in MW 1, everyone had heart and other hormonal problemsbut not Damon, it was his magnum dong that was affected, he needed release, he has to calm down sexually, he needed to sexually satisfied to not succumb to the side effects of the enhancement serum.
Thats the backstory. Now in MW3, Claire visits Rebecca, her sister, takes Damon with her, probably to clear hid mind, to avoid the sexual encounter but when she gets there, Rebecca suggests to have a drink and swim, unfortunately she give her bikini that is way too skimpy, Damon starts showing symptoms, worrying claire and rebecca, rebecca talks to him after the swim, tell him about he backstory, she shows him an aquirium where she administers a specific gas that makes the fishes horny and mate with each other, damon tries to touch the "tap handle" of the gas that was being administered to the fishes, Rebecca slaps his hands away. After a while she hugs him, the boy gets another symptom, he starts convulsing until she give him a serum of some sort to alleviate his "pain" but it looked more like she was taking his blood sample.
When Damon enters bedroom, he sees Clair, in that skimpy out, starts having sex, until she wakes up, she hesitates but she sees that he needs it, remembers the bond, starts stroking and orally pleasures him. Meanwhile Rebecca is examining the blood sample, it seems that when she slapped damon's hand the "tap/handle" broke off and she was exposed to the "horny gas", she isnt herself when she finds out her sister is sexually involved with her son/her nephew, she pounces on, orally pleasures him in front of claire and makes her have sex, until claire struggles, loses balance/falls and loses conciousness for a while, which results in Rebecca seduce and mate with damon, who despite Claire's protests, ends up ejaculating inside and his semen will fertilize her egg and end up making her pregnant, it is hinted that her being pregnant with damon's seed isnt just 'immoral' 'incest thing, it probably is even worse or something else.