I dont know if you are really aware of the weight of this comment for a lot of people. If the person you are observing is someone the MC can bone it will cause riots. It wont matter if its girl on girl or if its guy on girl, or if its a side chick people are going to be pissed.To give a better example, I'll tell you about a scene that's already written. There's a chance that the MC will arrive at a certain location, where he will hide and have the option to observe or not the scene that's happening in front of him. Because the player doesn't know what to expect, seeing a scene that might not please them can be avoided, but since it doesn't happen to him and is part of the plot, the scene will still exist.
It feels like the scene will be happening with a girl that has already been introduced as you are being obtuse about saying who it involves, and I really hope that isn't the case.