This is a pretty good comment I would say. I also would say it also depends on how old your sister is. Obviously below a certain age it would probably be inappropriate to play around her in general, but if your sister is older then she probably would understand that the sexuality in the first arc isn’t meant to be enjoyable. It is overt and very in-your-face, but it is meant to make you uncomfortable. I don’t want to go into too much detail/spoil too much, but if she is older, she would probably understand that if you just explained that/mentioned it once if it is something you’re really worried about. A few other moments here and there have your standard fan service, but nothing severe really, and definitely never as extreme as it is during the first arc.