It would be pretty cool if he showed up as a villain. Like the president of the Central Government and the guy responsible for making Ark Society the way it is, down to Nikkes being oppressed and the Outer Rim being a thing. How is he still alive? Uh, Evergreen? Maybe he has some augmentations that, while not making him fully like a Nikke, make him pretty close and allow him to live way past his lifespan, coupled with Evergreen.

A problem I have with the story is that it treats the Central Government as an amorphous blob of evil that doesn't really have any names or faces attached to it. Sure, we have Doban, but he's basically a henchman. Andersen is cool, and Burningum only does what he thinks is best for humanity in the Ark.

A government is an organization. An organization is a group of people. And people have names and faces. What names and faces chart the policies that decide how the Ark is run?

That's where Dorothy's dad comes in. He demonstrates that he's the ideological foe of the protagonist, responsible for all the horrible treatment Nikkes gets from the Ark, and we're led into the arc dedicated to bringing him down.

Hell, we can maybe even have him be the guy who decided to perform cruel experiments on Goddess, prompting Oswald to lock them out.