I'd really hate to make a dragon ball reference but it's the only similar situation i can recall.

When Goku went to meet Baba for the first time for a divination to try and find the last dragon ball, he had to do a series of trial or pay a ridiculous fee. The 3rd or 4th battle that took place (i can't remember) Goku had to fight some sort of demon that had the ability to amplify any sort of negative feeling inside a person heart and make them explode and Goku was immune because his heart was pure.


Boa beam seems to use a person's lust and turn them into stone that way. Luffy isn't lustful, his only fault is his obsession with eating. I can see why Boa is a shichibukai since her ability would be incredibly effective against almost everybody, but Luffy is a rare case so it is plausible for him to win against her (kinda like how his rubber ability allow him to be able to fight against Enel, who is actually much stronger than luffy at the time).