Crest of Toa was an artifact that increased a magician’s mana pool, allowing them to reach a much higher proficiency. In the future Shadow Labyrinth that Desir Arman came from, he was soul-linked to this artefact. It was the reason he was able to reach the Third Circle. However, Desir was not the first possessor of the Crest of Toa.
It was originally owned by some magician from Hebrion Academy and that magician was able to reach the Fifth Circle. Despite this, that magician had died in the Shadow Labyrinth and, due to his expedition group’s policy, it was given to the most appropriate successor, who turned out to be Desir.
There were two reasons why Desir was deemed the most appropriate to inherit the artifact. Firstly, Crest of Toa’s ability to increase one’s mana pool was greater for magicians of the lower Circles and, secondly, Desir’s analysis ability had gain notoriety within the expedition group. With the larger mana pool backing up his analysis ability, Desir’s contribution to the expedition was deemed irreplaceable to the extent that the plan executed nine years later would be impossible without him.