I went back and forth between 3/4 star for this, because although I liked this book when I was reading it, once I put it down I wasn't the most interested in picking it back up again.  I think this because although this is interesting it is a slower-paced book with layers, at first on the surface the story is about a boy and a cat going on little adventures to save books, the second layer is about the boy's grief over the loss of his grandfather and his depression and pulling away from everyone, but on the deeper third level, it is a commentary on the current world and our interactions with writing, books and publishing.  It gives commentary on the trend of reading for volume and not taking the time to absorb the work, never rereading, reading and collecting books for status, publishing books that are not good books but for the sake of profit, academics view and criticism of books and always wanting to be more efficient at reading.  These were all interesting, what made me decide on the 4 and not the 3 star was the last adventure, when Rintaro sees the outcomes of his adventures and the unintended consequences, I enjoyed that this book went further and asked questions about the fantasy and the ideal vers the reality and unintended consequences of his actions.  This self-reflection was interesting.  The reason this wasn't a 5 star for me, is as I wanted the adventures themselves to be a little bit more engaging harder for Rintaro to convince people to save the books..