@Silenthunter: The scene will only activate if the love interest currently prefers topping. All you have to do is buy the vibrator and the scene will happen automatically the next time you take the guy to the love hotel. Also don't worry too much about whether or not to use the toys, the guys preferences are completely unaffected by them.
Preference is solely decided by whether Haato starts the sex (this decides dominancy or lack thereoff) and what position Haato chooses when he does initiate it (decides if they prefer topping or bottoming), though it may take several attempts to get the guy to develop the preference you want and it gets harder to change as time goes on. Hope this helps!