Nine Lives (ニャインライブズ Nyain Raibuzu, ニャイン being a portmanteau of ニャア Nyā and ナイン Nain) is a group comprised of nine Cait Sith created by Nina Shitori.
Z/X Encyclopedia Entry
The system created by Nina Shitori by using her status from the privileged class granted by Four Archangels - Gabriel. Its content is to gives the 9 Cait Sith whom she has personally admitted authority equal to an average Guardian.
In the White World, a pyramid-like hierarchy is established with Angel at its top, and the Cait Sith's class is positioned at the very bottom just above the human. Since this order doesn't usually change, the "Nine Lives" system is a particularly special exception, and has inspired the Cait Sith that lacked sense of responsibility and personal ambition. As the matter of course, the Cait Sith's attention towards Nina Shitori also increases.
By the way, there is a campaign to collect scattered coins all over the world to gives the Cait Sith a "definite position" under the leadership of King Mike. However, since it was not officially recognized by Gabriel and the Twelve Apostles from the beginning, the possibility that the promise will be fulfilled even if the person who accomplished it appeared is abysmal. In fact, the participant is zero. Talk about King Mike's awful treatment.