Neutral good monsters are nearly impossible to write antagonistic adventure hooks for. (“He’s devoted to helping others! He must be stopped!”) A neutral good CR 26 outsider, exponentially more so. (“He’s an immortal champion of peace, kindness, and forgiveness! He must be stopped!”)
Thankfully, the empyreal lord Korada gives GMs an out: He’s a monk and a martial arts master. Which means that there are plenty of reasons PCs may seek him out and vice versa: to test their worthiness, to learn a new fighting style, as the last trial before becoming grand master of a monk order, etc. He’s also got the gift of foresight, so perhaps he has reasons of his own to fight the party—maybe to temper their steel, teach them humility, distract them from a path that will lead them to ruin, or even injure them so that they cannot attempt a trial above their abilities.
And yes, he’s part monkey and has a dash of trickster in him…so he might just aggravate PCs into fighting him for kicks. You can't trust monkeys, even monkey empyreal lords.
On their way to face one of the terrifying rakshasa rajadhirajas, adventures take a detour through Nirvana. On the grounds of a city-sized palace, they are pestered by a vanara four different times in four different gardens—always while they are trying to solve some puzzle or fend off an attack. Finally, they must fight the vanara himself. The monkey man is in fact Korada, and the four trials (and his jibes) were meant to prepare the adventurers for their fight against the nascent rakshasa immortal.
A powerful monk failed to challenge his master before the old man died in his sleep. So while the monk may be the most powerful of his order on the continent, and perhaps even in the world, tradition denies him his master’s title. He and his adventuring companions must thus seek out Korada himself. Only after facing the empyreal lord in single combat and using a move the agathion has not seen will the monk be able to take his master’s place.
On their way to confront a devil, adventurers are faced with an unusual antagonist: Korada, the Open Hand of Harmony. He asks the adventurers to turn from their path; if they refuse, he regretfully begins combat, pulling no punches. The devil is a fallen angel that Korada is determined to redeem…and if the adventurers dispatch him before his conversion, the devil’s immortal spirit will be lost to evil forever.
—Pathfinder Bestiary 4 90–91
Neutral good or not, any creature that casts mad monkeys (see Ultimate Magic) at my PC is going to die. (Primates set off my uncanny valley alarm. Also they throw poo.)
More on Korada’s worship and boons is in Chronicle of the Righteous.
My first exposure to the monk class was in Best of “Dragon Magazine” Vol. III, courtesy of “He’s Got a Lot to Kick About” from Philip Meyers, which offered ways of reworking the rather insane 1e AD&D monk class. I still don't know much about the class as it was written, but I gather that above certain levels, monks actually had to compete with other monks to advance—that was actually a required mandate of the class (along with level freezing for failure)! Obviously I don't want to go back to those dark days…but every five levels or so...? Might be a fun role-playing thing. And it seems perfectly reasonable that to achieve the level of Grand Master of Flowers, a 20th-level monk/champion might have to go a few rounds with the lord of the Dream Lotus. Old-schoolers in the audience, what do you think?