how to get the AV scene of Kasumi?
if you Sneak inside in her butt, u gonna end up inside her Nuts... doesn't make sense
Make a separate save, enter her testicles and make her nut in class (something she REALLY doesn't want to do). She'll take you to the school restroom. Quickly escape here, then make your way back to where she's seated in class and talk to her/walk into her.
Repeat this process and you'll notice she gets increasingly angry when it comes to reclaiming the player character.
Eventually a threshold will be reached and instead of forcing the player character down their shaft, they'll say they no longer deserve to be stored in such a clean area and will instead shove them up where the sun don't shine at which point the escape sequences will now be more similar to her mother's.
Edit: The time you have to get her to nut in class is on a time limit. If you take too long the class will end and the day will proceed to the next time block / location.
