You could actually call this volume “Senlin Ascends Further“ as this is indeed what our hero does, both geographically and climbing further at the tower and also socially by inadvertently becoming captain of a pirate airship and leader of a band of brigands. The story continues with Senlin still pursuing his intended - very commedable, although from what we have seen of her she seems to be managing fairly well. The Sphinx of the title is an oracle that may be able to help in the quest but things don’t quite go to plan and a major fracas ensues.
There is plenty more inventive world building and lots of action, but also underpinned by some serious thought given to how such a large tower would impact it surrounding environment and weather patterns. So more of the same good quality fantasy steampunk fare.
I have not (at time of writing this, in August 2025) moved to the final volume, I needed a bit of break from the rather intense narrative but fully intend to complete my reading at a later date and see if our lovers are finally reunited.