Planes

Planes (星層), or the three worlds (三界) principle, are realms identified by the Septian Church.

In Septian cosmology
The Septian Church states that the world consists of a number of planes situated on top of one another. Generally, it distinguishes three main planes with countless other planes (界) in-between them: The majority of the games take place in the middle plane on the continent of Zemuria. Exceptions exist, however. Phantasma, the main setting for Trails in the Sky The 3rd, is a world that belongs to a plane (次元) between the highest and the middle one. It was created thousands of years before the Great Collapse and start of the Septian Calendar. It served as a self-organised world designed to realise the creation of possible other worlds as desired for by the Ancient Zemurian civilisation that inhabited the Liber Ark. Specific examples of phenomena from the Beyond that the Church has attributed to the Goddess include the planes of existence.
 * The top plane is the sky (空), where the Goddess dwells;
 * In the middle is the earth (地上), where mankind lives;
 * At the bottom lies Gehenna (煉獄), where sinners are judged.

The planes are first mentioned in Trails in the Sky The 3rd, where Squire Ries Argent explains that the plane of humanity, equated to the continent of Zemuria, is a relative low plane of existence. She cites a Testament: "Our world and the world of the Goddess will forever be separate; She simply drops pebbles from above, known as miracles..." .

Other Planes
There may exist other planes that lie in between or beyond those mentioned by the Septian Church, such as the realm where Cryptids originate from or the extradimensional space found in the Old School House and the Realm of the Great Shadow. The dimension where the Liber Ark is sealed may also be such a realm.

The Spirit World is visited numerous times in Trails of Cold Steel IV. This realm seems to exist parallel to the physical world and has a red hue throughout. During the events of this time, demons are mostly seen and fought within this plane.

Mechanics
The games distinguish kinds of enemies according to this principle.

The monsters that roam on the human plane demonstrate no weaknesses to the higher elementals: time, space and mirage. In other planes, such as the world of Phantasma, enemies consist of fiends—creatures that cannot exist in the human plane—that do possess weaknesses to these higher elements.

Phantasmagoria, the final dungeon of The 3rd, is modelled after the High Seat of the Septian Church in Arteria. Unlike the prominent within the seven planes of Phantasma, the enemies in Phantasmagoria are linked to the angelic orders, including:
 * Blade Angel, a maiden who defends heaven, supports and attacks. Eldest of three sisters.
 * Arrow Angel, a maiden who defends heaven and supports allies, the second eldest of three sisters.
 * Rod Angel, a maiden who defends heaven, supports and uses arts, the youngest of three sisters.
 * Heaven's Proclaimer, messenger from Heaven that proclaims the end of an age and calls allies and explodes on death.
 * Tildawn, Guardian of Heaven that can see sin and judges the sinful, and delivers punishment to them, also appeared in the Spirit Shrines of Cold Steel II.
 * Rose Cherubim, an angelic statue that guards holy places. Seals foes' movement with icy stares.
 * Sleipnir, two-headed tank that guards Heaven and soars the skies and scorches the earth down below, after which an Ouroboros-made archaism is made.Sleipnir Concept Art (Sen IV).png