Hm guys, about the blackmailing... I got pissed myself at the beginning but :
Mc don't care, he mostly let her think she is controlling him, roughtly he play with her childish behaviour and gonna take advantage of her in the future (and it's happen somewhat in this version when he force his way to service his "goddess" during the massage), also the scene when he speak with the mother about him walking in his half-sister room was enough to tell that the blackmail gonna have zero bad consequence. So he is just playing along and maybe have more interest to let her have such "precious" proof, in case she want to watch the image/video from her side for exemple or because he want to turn her on because she fantazise about having power over him.
Also it's more like a brother sister game : one did something "bad" and the other say "Ohhh I gonna tell it to mom... Unless you (etc)" without having the intention to do it, but still gonna expect the counterpart, because this time he got the upperhand. But to be fair : I didn't try to skip her chores, as I was expecting some gain doing them. Maybe if you don't you get some others scene.
Also, I don't think it's weird to have a massive erection when an attractive women hug you (even more in night dress - iirc this part of the game), this just proving one thing : hormones are working. So this is just "healty" not "creepy".
For the dev (if he is around) please don't be pissed by this flood of bad comments, I personally really enjoyed your game so far : ) and I think the MC is one of the smartest one I have seen in an adult game.