I have a great idea for an h-game.

2
Takerial Lovable Teddy Bear
So in it. Your (step)sister is obsessed with you. And has just turned 18. She is now actively pursuing you. You are set to leave to your own place in two months, so the point of the game is to try and avoid her advances until you move out.

You have to adventure around to get information to be able to complete certain challenges for each week. (like rubbing sun tan lotion onto her.) Until you complete the challenges for that week, she uses her (step)sister incest powers to reset the week until you do.

Besides the challenges, she will be actively pursuing you. You also have to take care of your needs. So if she catches you alone in the bathtub it's game over. So you have to learn her schedule and use tactics to do so.

The scenes come from failing a certain way. As you make progress, the scenes get better. Each time you fail, you are caught by your Dad or (Step)Mom and thrown out to die on the streets in increasingly funny ways.
1
623 FAKKU QA
So it's kind of like those scenes in action or RPG H-games where the game over screens are the heroine getting attacked by monsters or whatever except in this case it's your sister? I can dig it.
2
luinthoron High Priest of Loli
Like Monster Girl Quest, you might just want to go for each game over anyway. :D
1
That's actually pretty awesome. I find it fairly humorous.
1
Gravity cat the adequately amused
So, it's basically a horror game.
Except instead of a monster trying to kill you, it's a semen demon trying to milk you.
2
raikura Deloused
liking the idea. thoughts on a spin-off: lose the step designation and adjust the age by a couple years.
1
More details are needed. If the stepsister can rewind time and force you to complete a challenge, why can't she rewind time to stop your parents from catching you doing naughty things with her? Does she already have a love nest prepared, so the moment your parents throw you out, she can swoop in and have you as a prisoner in its sex dungeon, forced to spend your every waking hour tending to her?

Are there other girls you can hookup with, and how do you stop the stepsister from going yandere and killing these girls? Maybe she made a deal with the devil to get her superpowers, and a term of the deal is she must refrain from killing her romantic rivals out of sheer jealousy? Will the devil be a girl you can hookup with, allowing you to turn the tables on your stepsister, and make her a prisoner in the sex dungeon she prepared for you (though I doubt she'll resist much in that case)?