Just cleared level 10 of Serena's scenario.
For Serena's scenario, level 1-5 is the side story, while level 6-10 are challenge stages against a high-level Serena but with hardly any story. (I believe the composition is the same for the other maps.) Overall the stages are not too difficult, but a few times I got beaten because of the unfair set-up and bad luck. After losing, I can check out what I am up against (Record -> Ceptor tag lets me see the AI's book) and build a book specifically to counter the enemies, so I can usually win on the second try.
For clearing the level up stages, I get new book covers (at levels 5 and 10) besides a crown mark on the map.
Serena's story was quite entertaining.