Rocksea arc (4)
Set in Rocksea, the outskirts of Andromeda system, this arc deals with various characters who make their home in this region.
[Rocksea arc]  [Duchess' boobs] 
Ehka had been a minor character that showed up in more than one story. Her first appearance is [Juron arc]  [The mad and the crazy] . Her career goes downhill afterwards. She also makes an appearance in [Ashuta arc]  [A date with the crazy] . You may notice a pattern here. And then her final appearance as a minor character is in [Milky way arc]  [Flawed system] .
Now, she gets her own story as a main character. This is her reward, I suppose.
In order to fully understand what is going on, you need to read through a bunch of stories, especially the ones mentioned above.