The Interstitial Sea is a threshold location in Agartha’s hidden world: reached through the ancient liquid Vita-aqua, it leads beneath the surface and later becomes the setting for a meeting among Morisaki, Shin, and Asuna. The text presents it not only as a destination within reach after a long approach, but also as the point where the three characters confront what comes next.

Setting and Properties

The approach to the Interstitial Sea passes through an ancient corridor, its worn stone still in good condition despite scattered plants. There, a man recognizes that the sea is finally within reach. The description makes the place the goal of a difficult approach without specifying its full geography or how far the corridor extends.

Access is through Vita-aqua, an ancient liquid described as having almost no buoyancy. Morisaki explains that a person can breathe when it fills the lungs and that Agartha lies below it. The water therefore works as more than a physical obstacle: entering it is the means by which Asuna crosses into the hidden realm.

Entry into Agartha

When Asuna answers Morisaki, he offers her his hand and leads her into the lake of Vita-aqua. She takes his hand timidly and follows as he wades farther in, with the liquid rising to her chest. She struggles somewhat, but Morisaki continues ahead. The scene makes the crossing a guided passage: Asuna enters an unfamiliar environment by relying on Morisaki’s knowledge and assistance.

The explanation of Vita-aqua establishes the relationship between the liquid and the world beneath it. Agartha is not merely somewhere beyond the shore; it lies below the substance through which the travelers must pass. The Interstitial Sea thus marks a boundary between the surface journey and entry into Agartha, while the unusual properties of Vita-aqua make that boundary traversable.

The Shore and Its Narrative Role

Later, Morisaki, Shin, and Asuna are together again at the edge of the Interstitial Sea, facing one another beside a spring of Vita-aqua. Shin asks Morisaki what he intends to do next. The scene does not provide Morisaki’s answer here, but the location gives the question a clear setting: after the journey through Agartha, the characters meet at the same threshold associated with entry into the hidden world.

The location’s appearances therefore bracket a passage into Agartha and a later moment of decision. First, Vita-aqua carries Asuna downward under Morisaki’s guidance; later, its spring stands beside the three characters as they face an unresolved future. The sea’s significance lies in this combination of physical passage and narrative threshold, rather than in any detailed account of its landscape.