What, in your opinion, is the type hardest type of power to give an জীবন্ত character without overpowering the character?

Hypnotization...that's always overdone...
Oh and the ability to one-up a level every time the protagonist meets a new antagonist -_- It's why আপনি know characters like Ichigo from Bleach অথবা Natsu from Fairy Tail will never lose.