Hourin's role *spoilers*

[zitch]

To me, the slaying of Hourin is unfair to her, but Gekkei was justified politically to do it.

Here's the scenario as I can tell at that point:

1 - The people are generally ignorant of the finer details of the God-Government systems, especially the very small detail that the kirin does not actually choose the King, but receives a relevation and is drawn to the chosen king by Tentei. This fact would probably only be known by the king and kirin himself, even, given what I've seen from the first Taiki arc. The people in general probably then believe that it is the kirin's choice who is king then. It's highly possible Gekkei himself believes this.

2 - If the people believe the kirin is the one who chooses the king, then they would generally believe it was Hourin's fault for choosing two lousy kings in a row. Nevermind the possibility her third relevation might actually produce a good king, the people would be highly distrustful of the third king, at the very least. There might be open hostility towards the governing system though. People as a whole aren't a rational creature, and I can see the sentiment going around: "Her first king was horrible, her second was a butcher. How can her third be any better?"

3 - Gekkei himself would then be a target of the people's ire if he did spare Hourin's life. So would any other leaders to took part in the rebellion. "She cannot choose a good king! Why spare her?" The distrust of the people might be much more damaging then the longer amount of time it would take to gain a new ruler after just killing Hourin.

In Keiki's case, his first ruler surrendered her life, and Youko still received hostility from her ministers for being Keiki's second choice and a female ruler. The world of the Twelve Kingdoms isn't a fair system to individuals. Ignorance is one major reason why.

[Shokou]

My point is that people's ignorance is a thing that can be supressed within the first few years of the new rule, as Sekishi did. And remember, people are always shown to be happy when a new king is chosen, because the youma is cut.

In regards to Gekkei, I refuse to believe he is ignorant of the heaven's rules in the world of Juuni Kokki. However, as he said, he was droven by his teacher-appreinticce love towards Retsu-ou. He could care less about what people would think, if he didn't even want the throne in first place...It was all Kyo-ou's plot, anyway.