Aeternus is a Legacy which gives ability to move back and forth between ages that have already been lived. With this Legacy the Garde can dramatically extend the length of their life. It is said to be a rare Legacy.
Ella was born an Aeternus. In Spain, Ella is taken in by the Santa Teresa orphanage as a seven year old in order to gain Marina's trust. Reverting to a younger age, and therefore size, Ella is able to move around the orphanage without being noticed and hide in small spaces. Ella often becomes a younger version of herself when she is scared or intimidated.
Setrákus tells Ella that he is also an Aeternus and hints that he uses it to keep himself young.
Perhaps one of the only things that Crayton was truthful about, the Elder known as Loridas (during the Lorien Era at least) did, in fact, have this ability. During a meeting with the Lorien Era Pittacus, regarding the execution of Setrákus Ra, Pittacus uses his Ximic Legacy to copy Ra's Dreynen, removing Loridas' legacies and causing him to return to his true age.
- It is said, by Crayton, that Loridas was also an Aeternus. He had told Ella that she was the tenth member of the Garde and that she was the one who would take the place of Loridas, these later turn out to be lies, however Loridas was Aeternus.
- In Latin, Aeternus means "Eternal"
- The fact that there were three out of ten Elders who were able to use this ability suggests that three of the new Elders would also be Aeternus. This would include Number Four (Ximic) and Number Ten - the tenth child who would have inherited the seat of Setrákus Ra had it not been removed. The Third Garde has not been revealed.