Sai Taker - Futari no Artemis 1-2

In the future, an energy source called Life has become incredibly important. Certain people are able to synchronize with devices called Sai which gives them the ability to extract Life and have super powers. These people are known as Sai Takers. Within the Sai Takers there is an even smaller group, Original Takers. Original Takers have a contract with a magical device, and they can manipulate Life without the use of a Sai. These powerful people are also immortal, only dying if they run out of Life. The world admires Sai Takers, but Original Takers are careful to keep their identities secret.