The Water Apparition That Cries 'Hyoi, Hyoi'. The name "Hyousunbo" is said to come from the "hyoi, hyoi" vocalizations it makes while swimming^[1]. Throughout Kyushu, kappa are called by various names such as "hyosube," "garappa," "kawantaro," and "kawappa," with hyousunbo being the specific Hyuga dialect form. In Kagoshima, kappa are called garappa, and in Hitoyoshi (Kumamoto), mountain spirits are distinguished as yaman-taro and river kappa as kawan-taro. Thus, the kappa of southern Kyushu are conceptualized as spirits that travel back and forth between the mountains and the water.

The Promise of the Hyosubo Rock ── A Legend from Togo-cho, Hyuga City. The Shiiya River in the Warabi district of Togo-cho was feared as the habitat of the hyousunbo, which drowned children playing in the river^[1]. The troubled villagers made a pact with the hyousunbo: "You will not take the lives of the children until a certain rock by the river completely rots away." The hyousunbo touched the rock countless times with its hands to check if it had rotted, and over many years, the rock became polished and smooth from being rubbed. The villagers called this the "Hyosubo Rock." It is said that the rock was buried during river improvement works in later years. It is a tale of negotiation with a water god, strongly rooted in the local area, featuring a "promise" exchanged between a kappa and humans, and a rock as proof of that promise.

Seasonal Migration Between Mountain and River, and Water God Sumo. The hyousunbo was believed to travel along waterways, living in the river from spring to autumn and moving to the mountains in winter^[1]. This connects to the folk belief in southern Kyushu that sees kappa as entities whose forms change seasonally between water gods and mountain gods. At the "Suijin-buchi" (Water God's Abyss) of the nearby Tsuboya River, it is said that sumo matches dedicated to the water god were held every year. This is an example where the nationwide concept of kappa loving sumo overlaps with local rituals to pacify the water god through sumo, indicating that the hyousunbo faith was not merely a ghost story, but one intertwined with water god worship.

Hyousunbo Within the Kappa Lineage of Southern Kyushu. Hyousunbo is positioned within the broader kappa lineage of southern Kyushu, alongside the garappa of the Sendai River in Kagoshima and the garappa/kawantaro of Yatsushiro and Hitoyoshi in Kumamoto^[2]. All of these share common traits: dragging people and horses into the water, extracting the shirikodama (a mythical organ in the anus), loving sumo, and migrating between mountains and rivers with the seasons. Among them, the hyousunbo stands out as a prime example of the regional diversity of southern Kyushu's kappa culture, possessing details unique to Hyuga, such as the origin of its name from the "hyoi" cry, the promise of the Hyosubo Rock, and the dedicatory sumo at the Tsuboya River's Suijin-buchi.