Tritheism (三神教) is an old religion that worships three deities: Hols[1] or Horu,[2] the sky god (天空神ホル); Grattheos, the sea god; and Maia, the earth goddess.
Tritheism predates the Hieroglyph Church.[2] Tritheism is mainly practiced in the Orietta Region and northern Afroca.
Ys VIII: Lacrimosa of Dana[]
In the sidequest, Old Monolith, Griselda points out that the religion is similar when she hears of the Three Principles mentioned in the monolith called the "Truth of Eternia". The Three Principles is the Eternian theory of the creation of the world through sky, sea and earth. Sahad thereafter theorized that Tritheism might have originated in Eternia.
The monolith translates to:
All originated from an abyss-- The boundless sky spreading in all directions. In time, rain fell from the sky, giving rise to the ocean. In time, fire spewed forth from the ocean, giving rise to the earth and the Great Tree. By th power of the Great Tree, life was formed, evolved, and set foot on the earth. And life is nurtured still by the earth... One day, life must return to the sky through the Great Tree. Thus, life continues the cycle of evolution.