I have also experience this behaviour and hope it is intentional.

Definitely not a bug in my eye.

Attacking Riurry probably should not be a chaotic act in the first place though. At least not if you got the quest.

Attacking any non-hostile is and should be a chaotic act. If you chose to go the chaotic way then why should the white unicorn help you? The white unicorn is opposed to chaos. You going to it while chaotic is your mistake not the game's.

The point is I was not chaotic when talking to white unicorn first time, so I got the quest to kill black unicorn. Did so, and nothing else, but I was unable to claim the reward because doing the quest was chaotic!

Obviously Yrruir can't be that opposed to it, given that he explicitly asks you to kill Riurry.

Killing Riurry is not a chaotic act, I'm almost certain Ruirry is chaotic and killing chaotic monsters are lawful. Never does it(he, I don't recall the gender) ask you to perform any acts of chaos or become chaotic?

Killing Riurry is not a chaotic act, but attacking him is (because initially he's not hostile towards you). Killing him is likely a lawful act but at least for a chaos knight it wasn't enough to counterweight the alignment hit of attacking him. So net result was that I converted from NC to CN.

That is what you posted in your original post. You explained it very well then.Sorry, no need to become emotional. The point is you are asked to perform a lawful act and Yuruir doesn't like chaotics.

I'll spell it out, One could find a way to make Ruirry hostile without performing a chaotic act or become non-chaotic before returning to Yuruir.

P.S. Making Calm Monster work on him while not chaotic is maybe a good idea, in my mind.

have you tried becoming neutral and talking to him again?
i think he will reward you/talk to you again then.

I was searching for Yrriur/Riurry RFE's and came up on this one.

Can we implement a dialog option with both Hotzenplotz and Riurry "Do you want to inform <foo> of your intentions? (y/n)" which is available while the corresponding quest is active and will make them hostile if you choose "yes"?

I agree that attacking without any notice is not purely ok even you were explicitly told to kill someone by a lawful entity, but lawful r/p as well as Paragon of Order IMHO should be consistent with both these quests and current means to make a monster hostile without directly attacking it are hardly transparent for players without some knowledge.

A scroll of monster aggravation's name is pretty straight forward and I'm pretty sure that a player that reaches the glade has equiped an armor of hate before.

Yeah, it's a bit weird and arbitrary how certain ways to attack him are not at all chaotic and some are.

Right, so as a lawful PC I'm going to aggravate everything in Lawenilotehl to kill a guy. And then I accidentally kill a beggar and lose my platinum girdle. Best solution ever.
I've equipped an armor of hate exactly 0 times.

Equipping an armor of hate to enrage a pure evil being and kill it in defense to be irresponsible for the crime is pretty twisted logic. Simple "no, I don't want to listen to your offer, Riurry, I came to cleanse the world of you" seems to me relatively normal way to do business in a fantasy setting.

I'm not arguing this anymore, there is no point. If the Creator wants to make things easier for the so-called Paragon, I'm not against it. I simply pointed out that there are some straight forward solutions for the player against your argument that the player has to know to mistarget a non-hostile.

Killing Hotzenplotz or Ruirry are not platinum girdle requirements none-the-less. Just saying.

White unicorn is opposed to chaos and should be hostile to all chaotics.
Conversely, black unicorn is opposed to order and should be hostile to all lawfuls.
Of course if you are L+ and want those 7 potions then it has to be either very difficult or very expensive (in terms of alignment drop) if not outright impossible to get them.
L+ means you are lawful from the beginning till the end, save for a few minor chaotic acts. Killing a greater white unicorn is a *major* chaotic act and should have major consequences.

Going further in this direction, Hotzy should be able to inform the player of the dead glade at level 30 and a greater black unicorn that is "a powerful being of darkness, that seeks to bestow power for furthering the coming of chaos."
Depending on your alignment, either white or black unicorn informs you of his opposite side's location.

For neutrals, both unicorns should be non-hostile. Alignment drop for attacking a non-hostile monster should be adjusted to be equal to a fraction of alignment gain for killing a powerful and very chaotic being, so the net gain would be significantly positive.
The same goes for killing the greater white unicorn - massive alignment drop for the great prize. Makes sense I think.