#iwasnotd3ad

I don't have much advice for coming up with stories, a lot of it comes from realizing and dissecting what I enjoy. I like stories about abuse/power/control, complicated characters, familial problems, queer people/bigotry against them, and the intersection of all of those things. Almost all the stories I get invested in enough to make a comic draw from several or all of these things. I also just use narratives to work through personal struggles I have.

As for designing characters that are related, it's important to take into account more than just the markings/colors of the parents/child. With your examples of Sycamore/the King/Aster; Aster shares Sycamore's colors-scheme (blue-grey) but body-type wise is much closer to the King (very fluffy/bigger, has the little "bowtie" fluff under his chin. smaller ears.), though, he does share the sleeked back hairstyle of Sycamore.

Markings/colors can help reinforce blood relation, but physical traits should do that as well. I also do like to give children unique traits of their own (Aster's parallel stripe down his back/downward facing cheek fluff) that don't match either parent to make them not just like. the direct middle point between the two, sometimes resessive genes can appear without either parent physically presenting them (two brown eyed humans having a blue-eyed child for example)!

And would both of them make good kings? Would Lain continue to serve as a chamberlain, but for Aster?

in regards to the monarchy system—yes it's a monarchy because there's one guy at the head of everything (and his name is literally The King). However, I do not think he thought ahead enough to know how inheritance and lineage would work. All that mattered to him in the moment is that he was at the top.

Even if he had won and his system hadn't collapsed under him—I do not think the king would make either of his children the next king. He would likely just have another general take his spot. Neither Lain nor Aster would make very good leaders. I do not know where Lain would end up if someone else took the place of leader. Probably nowhere good.