How bored does not one, but two gods have to be to pull pranks on a mortal who's simply trying to go about their day in an already complicated world of pirates and the Marines. 
Penguin  and Shachi were growing restless in the underworld and decided to venture out to the moral world. They pulled minor pranks here and there until they came across a mortal with a particularly interesting aura. Not knowing much about auras, like Law, Penguin and Shachi followed you