The Trinity Seven are seven mages who each stand at the peak of their fields. Each world has it's own Trinity Seven. Each of the Trinity Seven have acquired the "Lost Technica/Last Crest" in their particular archive.
The Lost Technica or The Last CrestEdit
The Last Crest is the Ultimate Magic for each of it's respective Thema though the power is immense the consequences are very heavy. Tales said it's used in the beginning by seven greatest mages, to defeat the True Demon King and seal his soul in the furthest part of the world. Seeing the power, they decided that only one person should be able to use their ultimate magic. This is the beginning of Trinity Seven's system.
When using her Last Crest against Arbalisha, Yui reminds her opponent, "There's only one reason why everyone is so afraid of Trinity Seven".
Last Crest of each Archive can only be used by its respective Trinity Seven. This means no matter how deep a mage has done their research, they will never be able to understand that magic.
In case of Lilith and Anastasia, the world even decided to remove Anastasia because there can be only one Trinity Seven of Luxuria. Although, inconsistently, this doesn't happen in Liese Chronicle side story when she is transported to parallel universe and someone else holds the title.
The first shown Last Crest is Liese's Baal Peor or the Time Fissure in which she can create a super high-speed space that far surpasses reality's speed, when looked at it properly it is a pseudo-version of stopping time. The consequence is that the user will be stuck in the high-speed space for all eternity, until someone can release her.
Levi used "Leviathan" several times, but it's always a bluff or fake because she is always keeping her true power hidden from the enemy. Even during times when it seems hopeless, she still doesn't consider it worth showing her secret card.
PurposeEditThe Trinity Seven hold a destiny far exceeding their initial role, which is presented as merely being the greatest mages in their respective fields, this destiny comes into play when a Magic King appears
According to Hijiri when she was expelled from the world Arata is in, she was able to see the world from the outside and witnessed the world being destroyed when the magic king, in this case Arata, and the Trinity Seven come together. This is a cycle imperative to the reincarnation cycle of existence, they are born to destroy one world, after which a new world will be born in its place, which later meets the same fate.
According to Abyss Trinity, regardless of any circumstance surrounding him the Magic King will always end up encountering the Trinity Seven, and they will always play a role in helping him destroy the world. Some Magic Kings, namely Abyss Trinity himself, slaughter them and take their powers for himself, others, like Astral Trinity, will utterly dominate and subjugate them, there are even Magic Kings who work together with the Trinity Seven, who then willingly help him destroy the world. After the Magic King destroys the world, a new one is born.