Astral

Unreleased Archaeans are the summons of Final Fantasy XV. They are creatures who protect areas of the world from humans, whose powers can only be used by Noctis Lucis Caelum after forging a pact with them.

Titan is described as an "Archaean" on the loading screen of Final Fantasy XV Episode Duscae that gives a story synopsis, but the developers have referred to the summons as "Eidolons" in interviews. Though Ramuh is summonable in the demo, he is not referred to by any term.

Archaeans are a physical manifestation of the power of the stars and serve as the world's protectors; they defend certain areas from destruction by the activities of humans. A piece of artwork from the end of Final Fantasy XV Episode Duscae hints that the Archaeans are connected to the world's deities and the creation of the world itself. The summons are said to be intelligent creatures with their own agendas and language, and play an integral part of the world and its lore. They are said to be indifferent to the happenings in the human realm and humans cannot interpret their thought patterns as their behavior is very different from that of humans.

Gameplay
Archaeans are ranked in accordance with their size. For example, Leviathan is one of the highest-ranking and most powerful Archaeans available in the game due to its great mass. Only Noctis can call upon Archaeans, but he cannot do so in tight, enclosed spaces, such as the insides of caves. To obtain Archaeans, Noctis must defeat them in battle, or obtain them through other means. It has been said the player will get something for defeating the Archaeans to prove they beat them, and will sometimes get to "borrow" their power after doing so.

In the Final Fantasy XV Episode Duscae demo the Archaean appears to do its special attack once summoned before disappearing. It is summoned by holding the summon button when Noctis is at 0 HP. Whether this mechanic is planned for all Archaeans in the final game, or whether there will be different conditions for summoning each of them, is unknown. In the demo, just before the Archaean appears a health bar with 0 HP appears below the party's HP bars on the bottom of the screen. This could be the Archaean's health bar being disabled for the purposes of the demo, indicating Archaeans might be planned to remain on the field and be targetable by opponents in the final game. Enemies defeated by the Archaean in the Episode Duscae demo yield no EXP.

Ramuh
Ramuh is the Archaean available in Final Fantasy XV Episode Duscae. He uses Judgment Bolt to deal heavy damage to enemies within a wide radius. Ramuh can only appear before Noctis when he hits 0 HP.

When summoned, Ramuh grabs Noctis with his left hand, and he raises the staff he carries in his right hand into the sky above him, wrapping it in lightning. Ramuh throws his staff at enemies, triggering an explosion. After the explosion, the ground and all enemies are charred black, and Ramuh lingers for a while before vanishing. Ramuh's staff resembles Ixion, the lightning aeon from Final Fantasy X. His size is similar to the concept art of Ramuh towering over mountains for Final Fantasy XIII.

Titan
Titan is the Archaean who resides in Cauthess and plays a role in the main story of Final Fantasy XV.

Leviathan
Leviathan is an Archaean seen during the attack on the city of Altissia who will play a key role in the main story. Portrayed as female, Leviathan is said to be elegant, intelligent, and "very close to God". She can disguise herself and move around as liquid.

Creation and development
Leviathan was one of the first summons designed for the game, from when it was known as Final Fantasy Versus XIII.

The idea behind the summons in Final Fantasy XV is that they are not "random creatures" that only show up and suddenly disappear. The creatures were designed to fit into the world as beings that live there. Thus the "forging of a covenant" with one is meaningful. Director Hajime Tabata has described it in this way: "You get them to help you. You ask them to let them agree to help you. In the world of Final Fantasy there is one word given to them and that is 'Guardians.' They are protective deities. So the relationship that Noctis has with them is that he besieges them to request them to lend him their power."

There is said to be a story-based reason why the summons are traditional, familiar summons from the series. Because the summons play a big part in the story and are integral to the game world, the developers preferred to have traditional summons to see how they fit in the story, rather than having new summons.

Square Enix intended to make Titan the Archaean that players could summon in Final Fantasy XV Episode Duscae. In the end, however, Titan was replaced with Ramuh due to the former's story significance. Ramuh's inclusion is meant to show players what happens when an Archaean has been tamed and made available for use.