Ok, I’m done with the last volume, and boy it was good too! Really strong finish for the series.
I liked that the book is not there to give redemption to 智恵子, like I feared. Instead, it put emphasis on the fact that she made her choice. There was no way for someone in their right mind to do what she wanted to do. She did it anyway, just pretty much giving up on most of her humanity on the way. And it’s nice that, despite all that, she still gets on better terms with 栞子 and even recognize (to some extent) the worth of 大輔.
Anyway, this episode was also special in the sense that, for the first time since the first volume, the main characters are being personally threatened, rather than doing things for other people. And contrary to the first volume, which was a bit unrealistic, the threat here is life-destroying debts. That might sound bland compared to the enemies the main characters face in other light novels (Re:Zero comes to mind
), but it got me to relate way more to the characters than fantastic stuff.
Reading the あとがき, I was really surprised to learn that it wasn’t a given that ビブリア would become a series. Instead, it was mostly going to be a one shot at first. And, thinking about it, I guess it makes sense from the publisher’s point of view. Can’t really blame them for thinking that a light novel about classical literature would not sell like crazy. But that also made me realize something: 智恵子 isn’t mentioned at all in the first book. I would probably need to re-read it to make sure, though.
Instead, she is introduced in volume 2, starts interfering with the characters in volume 3, then confront them directly in volume 4. She somehow gets to accept (or at least not hard reject) the relationship between 栞子 and 大輔 in volume 5, and even help them in volume 6. Then volume 7 comes, basically giving us a lot more about her background and solving that problem, allowing a tense, but real, reconciliation with 栞子, thus closing the arc. 
I do feel like reading the “10 years later” book, now. I don’t know if the author will keep writing stuff in that universe, but that would be nice too. I also had a look at the other stuff from the author, but nothing is striking my fancy right now 