Each one is an Anchor of their home Loop and, due to the extensive time they have, they are considered far more powerful than any other 4D mortal. It is well known that any of them could Ascend if they choose, but they decide to remain as 4D mortals, because Ascending during the Loops is regarded as a BAD THING.
The Original Seven, or most of them, first met in the Potterverse when the Evangelion pilots deliberately crashed their loops using their EVA Units in an attempt to escape from said Loops. The Anchors then all found themselves on the Hogwarts Express in the same carriage as Harry Potter, the local Anchor. This is regarded as their first fused loop and an Evangelion FUBAR loop. The EVA pilots were then given an explanation about what not to do during the Loops.
Usagi Tsukino first met the group in a fused Loop in the Narutoverse. Ranma, Shinji, Ichigo, and Harry as well as other Loopers from their home Loops appeared with them, though it is questionable if some of the latter were Awake for this.
Usagi and Ranma were placed on the same team under the guidance of Anko, during which time she was tricked by their third team member in regards to sleeping arrangements.
It is currently unknown when or under what circumstances Lina became known as a Looper.
The Original Seven are very close to one another, almost as much as Loopers from the same universe are, due to the fact that they have had so many shared experiences.