this clod can be a real pain, huh?
Prior to ascending to the throne of Malkuth, the future Emperor Peony IX grew up confined to a manor in Keterburg. But this didn't stop him from sneaking into Professor Nebilim's classes and forming a close friendship with Jade. Jade is known as the emperor's right hand man, but their relationship is not exactly on business terms. Rather, it's one of mutual teasing, mostly on Peony's part. While Jade usually only subtly insults Peony's lack of organization (notably, Peony's giant pile of junk in Jade's office and a castle where rappigs roam freely) and philandering ways, Peony seems to be the only person that can effectively get the best of Jade. And that? Is something that no one else seems to manage. This ranges from insulting Jade's fashion sense by providing him with a new outfit after completing the singles tournament in the Baticul Coliseum to outfitting him as an "Evil Fonist" when giving the party their badass "Final Battle" costumes. And we never got to see what was under that bathrobe... anyway.
The Emperor also took it upon himself to name his pet rappings after some of the people closest to him, including Jade. When the party is sent on a mission to round up runaway rappings, Peony expresses his worry over his "cute little Jade" being cooked in the kitchen, much to Jade's annoyance. (Jade also mentions at one point that Nephry was Peony's first love, and he finds the care that Peony shows to Nephry!rappig is somewhat disturbing.) The relationship between the two was a bit startling to the party when they first met Peony, mainly because the emperor casually asked Luke if he and his companions were responsible for "dragging my Jade all over the place," and berates Jade for managing to get his fon slots sealed.
However, the relationship between the two certainly runs deeper. Nephry mentions to Luke that Peony was responsible for changing Jade's views on the replication of living things. It's also clear that Peony trusts Jade; not only does he entrust Jade with bringing a letter of peace to Kimlasca, but he allows the Colonel to serve as an representative of Malkuth throughout the game. Peony is also the only one who believed that Jade was still alive following the collapse of Akzeriuth. The two have an obvious bond and are able to actually understand each other, and I have to say that no other character in the game is able to completely understand neither Jade nor Peony.
The two may tease each other (and certainly have some interesting ways of doing so), but they're clearly best friends.