Dunno how I feel about calling this a "side story"... It's more like "Season 2"
Yeah it does feel a bit more like S2, but given the short length of the other side stories who knows how long this arc will be.
I do think, if you ended it when Aster was (re)-born, then you could honestly just have the completed story without a need for additional chapters. So it does make sense that this isn't quite S2. But I'm enjoying and chewing it up, I want to see a more grown up Aster!!