When you've already picked where you'll live, who you'll live by, AND who you with show or affection/be dominated by when you move to gensokyo. Also, not taking into account the resident vampire and her sadistic maid, a psycho shrine maiden and her cronies, a lesbianic pair of witches, AND anything else that has the potential to eat, maim, burn, drown, freeze, or impale you... including your lover and/or dominator. Whichever you chose. AND if you have ever said to your self "I wouldn't mind being biten by remilia..."
EDIT: I forgot to say that you might get kicked in the crotch. Most likely by Tewi.