I knew someone who had crabs once… They had to shave their pubes and apply topical cremes!
Damned crab-people.
I’m really sick of you guys getting off topic with something as silly as crab people.
Back to the original question: ninjas do not need juice because they possess supernatural powers. They get lots of cardio running around on rooftops and doing secret ninjastic shit. Most importantly, they could kick the crab people’s ass! 
…only because crab-people are a bunch of metros
i disagree. the crab people far outweigh the ninjas in numbers and therefore would prevail.
But ninjas are TOTALLY SWEET!
Plus they have their allies, the hippos!
Crab people have no friends.