Argres

Argres (アルグレス), known in its cursed form as the Nameless One (名も無きの聖獣) and the Black Holy Beast (黒の聖獣), is the Holy Beast that guarded the Sept-Terrion of Earth.

Background
Around S.300, Argres takes on the majority of the Erebonian Curse from Ishmelga; together with the Primal Ground copy underneath the Heimdallr Cathedral, it is translocated to an area northwest of Heimdallr. Along with the Primal Ground, it was corrupted by the Curse and lost both its name and form.

In, Argres is summoned once more with the appearance of the Gral of Erebos by Black Alberich, who intended to have it killed in order to release the bulk of the curse it stored by using an Originator Zero, a homunculi created by the Black Workshop. Crown Prince Cedric attempted to choke Altina Orion, who was the last model of the series to do so, but when he was interrupted, Argres (called the Nameless One) went on a rampage. Altina's "sister", Millium Orion, attempted to fight it, but was quickly overpowered and fatally wounded, transforming into the Sword of the End.

Rean, seeing his classmate die in front of his eyes, goes berserk, using the Sword of the End to apparently slay the Nameless One. This caused the curse it had stored in its body to be released across Erebonia and its territories, beginning the Great Twilight.

Purged of the curse, Argres survived its encounter with Rean, eventually nestling at the Sanctus Shrine on the beach near Aulos Seaside Way. In, Toval Randonneur and Class VII discover the shrine and investigate it, where they find Argres at the heart of the shrine. Upon meeting the group, Argres tries to introduce itself, but realizes that it has forgotten its name, and that it intends to remain in the shrine to see the Great Twilight engulf Zemuria, believing that it cannot be stopped. After Toval rebukes it for unwilling to help, Argres becomes intrigued and challenges the group to see if they have what it takes to change fate. To its surprise, the group manages to defeat it.

Although it expended the rest of its strength in the ensuing fight, Argres finally remembers its name and is able to convey it to others. Grateful, it bestows the Earthen Prison to Rean before fading away. Argres' Earthen Prison would prove invaluable in saving Rean, who would use it to expel Ishmelga from him as an incomplete Great One before the malevolent entity could fully corrupt him.

According to Roselia, the cryptid Zoro-Agruga is its "kin".

Trivia

 * Argres (Shiroki Majo).jpgs appears to be a direct reference to Shiroki Majo, the first game of the Gagharv Trilogy. In the game, one can find the Holy Beast Argres in the Lost Forest with permission of the Toneriko Village.
 * Laura S. Arseid remarks Argres' name is similar to the name of the Argent Divine Knight, Argreion.
 * Argres is the first Holy Beast in the Trails series to die.