Type Mercury

Type Mercury (タイプ・マアキュリー), also known as ORT (オルト), is the Ultimate One of planet Mercury, though Character Material states that it may actually be the strongest being on Mercury, and the fifth being on the list of the Twenty Seven Dead Apostle Ancestors. It left Mercury and accidentally landed in South America five thousand years before the Common Era in preparation for the "promised time" that occurs in Notes. The previous fifth Dead Apostle Ancestor sought to capture it and was killed by it instead, and a number of agencies have tried dealing with it only to be annihilated. It was decided that it was to be named an Ancestor after it was discovered to have vampiric properties. It has shown no interest in damaging or invading the surrounding world, and it will not respond unless it is disturbed. It is thought that it has closed itself off in its lair until the promised time. It was developed with the concept of "hopeless despair" much like a hidden boss monster in an RPG that's stronger than the final boss.

Abilities
ORT is around forty meters tall with a build similar to a spider. It is covered with an outer skin that is harder, more flexible, more temperature resistant, and sharper than any other substance that exists on Earth. It is an attack-type lifeform with offensive capabilities more powerful than any other being on Earth, allowing it to easily kill the previous fifth Dead Apostle Ancestor in seconds after being attacked, and it's very existence is above that of a normal being. It does not have Gaia's concept of death, which makes it immune to abilities such as Mystic Eyes of Death Perception. It can be said that it has no weaknesses while the battleground is Earth, though like other Ultimate Ones, it can be stopped by certain concepts and abilities such as True Magic. It is able to partially simulate the creatures it preys on, allowing it to potentially mimic human speech if it devours a human. It cannot actually learn the culture of Earth, so it would simply remain as an imitation. It has found that the creature with the "strongest flavor" is the previous fifth Ancestor.

ORT's very existence affects the reality surrounding it, similarly to a Reality Marble, but on a completely different level. Crystal Valley (水晶渓谷), a name developed by Earth's magi, passively transforms the area around ORT into an alien crystalline substance, said to be beautiful, but horrendous and disturbing at the same time, that presumably exists on Mercury. If Earth is considered to be a massive Supreme Reality Marble, then Crystal Valley, as an "Innate Bounded World", is leaking an "alien system" to rewrite physical laws in order to create an imitation of the Supreme Reality Marble of Mercury within a small space. The ability is supposedly activated by ORT's movement, and the area around it has developed into a structure resembling a spider's web with crystal towers formed from trees.