Seal (World)

The Seal (異界) or the Otherworld (異界), also known as the Underworld (冥界) is a Demi-Material World that overlaps with Spiritual Worlds such as the Elemental Realm and the Daemon Realm, in which the Spooky Palace is located and where Aggressors live.

The Otherworld is said to be a Parallel World of the Daemon Realm, and can also be accessed through "Underworld Gates".

Characteristics
The Otherworld is bigger than the Universe, with conditions akin to the outer space where traditional notions of up and down, earth and sky, do not apply while gravity is absent entirely.

Instead, this realm consists solely of objects composed of densely concentrated Magicules, scattered throughout the expansive void. These objects possess remarkable strength, comparable to the resilience of Magisteel, and have the inherent ability to generate formidable gravitational forces.

Consequently, they have been meticulously processed and adapted for use as foundational structures known as 'Bases' (拠点). The former inhabitants of the Otherworld, the Phantoms, relied upon these bases to maintain a semblance of life reminiscent of their experiences in the Central World, ensuring they did not forget the familiarity of living within a gravitational field.