It is believed that the Animus Vitae energy that gives the Pandora's Box Aniform creatures their life-force (and the term Aniform) is present throughout the universe, but is nearly undetectable by modern science. Pandora's Box, created in forgotten antiquity from Animus-charged stone, was compared to an ancient radio that was able to tune into the frequency of Animus and use that to draw in the creatures. The creators of the Box gave it a sort of fail-safe mechanism should it be re-opened: whoever opened it would be "branded" with the Signet, conferring them an ability to manipulate Animus Vitae.
Animus Vitae can also be channeled and manipulated technologically without using Pandora's Box: Council of 98 scientists used Animus devices in their labs at Council HQ; the Black Order built portable Aniform Control Devices capable of influencing nearby Box creatures to ignore Order troops.
When an Aniform creature from the Box is killed, their residual Animus is severed and left behind. The Signet branded onto Deckard's arm by the Box allows him to siphon these clouds of Animus and use the energy. This primarily serves to heal him in combat and repulse enemies with the Animus Blast, but the Signet can also channel stored Animus outwards, permitting Deckard to charge devices in the story. The Animus channeling context-action can also be performed on Aniform Control Devices used by the Black Order late in the game, temporarily inverting them so nearby creatures will ignore Deckard and the Council and attack the Order instead.