Granted (this is hard without a specific character)...But, if there is a romance that that character is involved in then someone you strongly dislike becomes said character. Or, you do things differently than that character and so screw up an otherwise awesome plot, possibly even allowing for the villain to win. And, to boot, someone whom you love in real life becomes the villain character. If you are a character like Naruto or Luffy or L, you find their eating habits make it very difficult for you to sleep at night and never quite feel 100% Consequently, eventually, someone discovers your secret (that you are from the real world and they are all just characters) and whatever government exists in said anime kidnaps you and uses you for godawful experiments in an attempt to get to our world. And whats worse, they succeed and use the unique awesomeness of their world to conquer ours and everyone you love suffers a terrible, if not fatal, fate. Thanks a lot, now all of us who knew their secret are dead and we've you to thank!
I with for the phenominal cosmic powers of a genie without the restrictions of being a genie.