A young girl trapped in a box who also happens to be the key to saving all the worlds. No biggie.

Really all that is known about her is that she's important for the survival of all the alternate universes. She used to be a real girl but something happened to her that put her conciousness into a box. Since everyone has different versions of themselves running around in the alternate universes it's up to the Seekers to find an alternate version of Pi and bring her back to the Spire so that the version in the box can be downloaded into the body of this other Pi. Download Pi into any other body would just destroy the both of them.

As the last Keeper of the Spire, he watches over Pi's box and sends the Seekers on their missions. He seems to know much about the Spire but is reluctant to share most of that knowledge, insisting it is on a need-to-know basis. 

Not much is known about Zhu besides the fact that she is a very important person in her own world, a scientist who discovered the multiple universes and devised a way of accessing them.

She's the head of the Multiple Universe Exploration and Research Division, tasked with mapping out the different worlds and finding out as much as possible about them. That is the official agenda and the one followed by most of its employees, but Zhu herself has her own agenda. She knows about the Spire and the Seekers and her agents that are actively exploring the different worlds have a secret mission on the side: eliminate any seekers or versions of Pi they come across.

Kai should have been the leader of Kiro's team, or at least that's how he sees it. But then Na Kiro came along and ruined everything, and now Kai is stuck in the role of guard while Kiro calls the shots, and you better believe he's salty. Nobody really likes Kai, anyway. He's cocky and volatile and nothing good ever comes out of his mind.

Still, he did think of the term 'shifters' for the ExtraUniversal Quantum Shift Generators and that has to count as some form of achievement.

From the moment Zhu's findings on the multiverse were made public, Hana knew she wanted to be a part of that. Fortunately for Hana brains isn't all that's necessary in the Multiple Universe Exploration and Research Division, they need brawn just as much to protect the agents as they map out the different worlds. And of course for the more secretive mission of finding and ending the various Pi's in each world. Fighting Hana can do, and you do not want to be at the business end of her anything.

MJ was never supposed to be the science officer on Kiro's team, he was merely an intern tagging along. But when a malfunction in the previous science officer's shifter caused him to shift into multiple pieces, well, MJ was the only around qualified to take up the task. 

As far as MJ is concerned, all the QuSEF agents are concerned with is mapping out the worlds. He doesn't know anything about Pi or the Seekers.