>>103595070
Uta 3 spoilers for maybe 2 or 3 weeks from now.
Do NOT click if you are following Koyo's playthrough blind and want to experience the game together with her.

Raiko's primary motivation for having the Mikado killed and taking over is to liberate the people from human rule.
The Mikado has been abusing his "human privileges" hardcore for centuries.
He was controlling the civilization and cultural advancements, banning all research and development and so on, since progress could both endanger his own position and eventually steer the world down a path of ruin again if they eventually progressed far enough and happened to repeat old humanity's mistakes.
There's a lot of misery in the world and very easy solutions to it, but the Mikado has actively been working to keep that status quo both internally in Yamato and externally using Yamato's military might to crush other nations if they happened to make technological progress or stumbled upon remnants of old humanity.
With him as an immortal ruler they were basically all his pets, sometimes rewarded for the love and devotion they offer up to him, sometimes punished for stepping out of line, but always under his control.

When that anon was talking about Code Geass earlier it's honestly not far off the mark.
Raiko is very similar to Lelouch in a lot of ways, right down to being able to commit all sorts of atrocities and paint himself the villain for what he thinks, and looking at it objectively honestly just is, the "greater good".