Although the kappa is a formidable creature, it is incongruously small, usually no bigger than a human child. It might have a bird-like beak or a pointed mouth, but sometimes it has a face like a monkey instead. It often sports a tortoise's shell on its back, and its slippery skin is blue or green or sometimes red. Its precious head dish is usually surrounded by a mop of bushy hair, and some kappa have hair growing all over their bodies. The kappa's limbs are long and sometimes stretchy, and its fingers and toes are of course webbed, all the better to slip away into the murky depths of its watery home.
They are very proud and like to boast, but they are also very polite. They have a great love for challenges. They also seem to possess large amount of knowledge when it comes to medicine.
Their deep sense of decorum will not allow them to break an oath, for example; so if a human being can dupe a kappa into promising to help him, the kappa has no choice but to follow through.
They have an aversion to iron, sesame, and/or ginger.
They also have an unusual obsession over cucumbers... and any creature's backside.
It was believed that if confronted with a kappa there were a few means of escape: Kappa, for one reason or another, obsess over being polite, so if a person were to gesture a deep bow to a kappa it would more than likely return it. In doing so, the water kept in the lilypad-like bowl on their head would spill out and the kappa would be rendered unable to leave the bowed position until the bowl was refilled with water from the river in which it lived. If a human were to refill it, it was believed the kappa would serve them for all eternity.
A similar weakness of the kappa in some tales are their arms, which can be easily pulled from their body. If their arm is detached, they will perform favors or share knowledge in exchange for its return. Once the kappa is in possession of its arm it can then be reattached. Another method of defeat involves the kappa and their known love of shogi or sumo wrestling. They will sometimes challenge those they encounter to wrestle or other various tests of skill. This tendency is easily used against them just as with the bow, by encouraging them to spill the water from their sara.