The belief in this ball is rather mysterious, and scholars have come up with various explanations.
One explanation is the commonly observed “open anus” of drowning victims (as if something had been removed or sucked out).
Should you chance upon the quarrelsome Kappa, please remember to bow deeply.
If the courteous Kappa bows in return, it will spill its strength-giving water, making it feeble, and forcing it to return to its water kingdom.
For instance, the flesh-eating Kappa is mostly evil, but when captured, it will pledge to assist with farm work or to teach its captor the arts of setting bones and making medicines and salves.
The Kappa, however, is more accurately described as the Kawa no Kami 川の神 (River Deity), a term mentioned in the Nihon Shoki 日本書紀 (Chronicles of Japan), one of Japan's earliest official records, compiled around 720 AD.
After the water was drained, a pipe was stuck in the hole before it was filled up, so that Suijin-sama, who might have been trapped inside, could find a way out." Gabi-san also discovered a web site (no long online) claiming that this toilet-water Suijin takes the form of good bacteria -- bacteria that cleanses the water for reuse in the soil. , women have played an important role in the history of Suijin worship in Japan.
However, with the great influx of Korean and Chinese people into Japan starting around the 2nd century AD, and with the subsequent introduction of Buddhism in the 6th century, Japan’s many indigenous water kami began to slowly absorb attributes from these emigrants and from Buddhism.
Suijin are supernatural beings found in lakes, ponds, springs, wells, and irrigation waterways.
They are often depicted as a snake, a dragon, an eel, a fish, a turtle, or a kappa.